The increasing interest in mushrooms during the past few years has not been confined to the kinds growing spontaneously in fields and woods, but the interest aroused in the collection and study of the wild varieties has been the means of awakening a general interest in the cultivation of mushrooms. This is leading many persons to inquire concerning the methods of cultivation, especially those who wish to undertake the cultivation of these plants on a small scale, in cellars or cool basements, where they may be grown for their own consumption. At somewhat frequent intervals articles appear in the newspapers depicting the ease and certainty with which mushrooms can be grown, and the great profits that accrue to the cultivator of these plants. While the profits in some cases, at least in the past, have been very great to cultivators of mushrooms, the competition has become so general that through a large part of the year the market price of mushrooms is often not sufficient to much more than pay expenses. In fact, it is quite likely that in many cases of the house cultivation of mushrooms the profits are no larger, taking the season through, than they are from the cultivation of tomatoes or other hothouse vegetables. Occasionally some persons, who may be cultivating them upon a small scale in houses erected for some other purpose, or perhaps partly used for some other purpose, may succeed in growing quite a large crop from a small area with little expenditure of time and money. The profits figured from such a crop grown on a small scale where the investment in houses, heating apparatus, and time, is not counted, may appear to be very large, but they do not represent the true conditions of the industry where the expense of houses and the cost of time and labor are taken into consideration.

Probably the more profitable cultivation of mushrooms in this country is where the cultivation is practiced on quite a large scale, in tunnels, or caves, or abandoned mines, where no expense is necessary in the erection of houses. The temperature throughout the year is favorable for the growth of the mushrooms without artificial heating. It is possible, also, to grow them on a large scale during the warm summer months when it is impossible to grow them under the present conditions in heating house structures, and also when the market price of the mushrooms is very high, and can be controlled largely by the grower. For this reason, if it were possible to construct a house with some practical system of cooling the air through the summer, and prevent the drip, the cultivation in houses would probably be more profitable.

For the past few years the writer has been giving some attention to the different methods of the cultivation of mushrooms in America, and in response to the growing interest for information concerning the artificial cultivation of these plants, it has seemed well to add this chapter on the cultivation of mushrooms to the second edition of the present work. The cultivation as practiced in America exists under a great variety of conditions. All of these conditions have not been thoroughly investigated, and yet a sufficient number of them have been rather carefully studied to warrant the preparation of this chapter. The illustrations which have been made from time to time, by flash light, of the cave culture of mushrooms in America, as well as of the house culture, will serve to illustrate graphically some of the stages in the progress of the work. For present purposes we will consider, first, the conditions under which the cultivation is carried on, followed by a discussion of the principles involved in the selection and preparation of the material, the selection and planting of the spawn, as well as the harvesting of the crop.

THE CAVE CULTURE OF MUSHROOMS IN AMERICA.

This has been practiced for a number of years in different parts of the Eastern United States, but perhaps only a small portion of the available caves or tunnels are at present used for this purpose. These subterranean mushroom farms are usually established in some abandoned mine where, the rock having been removed, the space is readily adapted to this purpose, if portions of the mine are not wet from the dripping water. The most extensive one which I have visited is located at Akron, New York, and is operated by the New York Mushroom Company. In a single abandoned cement mine there are 12 to 15 acres of available space; about 3 to 5 acres of this area are used in the operations of the culture and handling of materials. The dry portions of the mine are selected, and flat beds are made upon the bottom rock, with the use of hemlock boards, making the beds usually 16 feet long by 4 feet wide, the boards being 10 inches wide. In this case, the beds, after soiling or finishing, are 9 inches deep, the material resting directly upon the rock, the boards being used only to hold the material on the edges in position. Figures 223 and 224 illustrate the position of the beds and their relation to each other, as well as showing the general structural features of the mine. The pillars of rock are those which were left at the time of mining, as supports for the rock roof above, while additional wood props are used in places. In this mine all of the beds are constructed upon a single plan.

At another place, Wheatland, New York, where the Wheatland Cave Mushrooms are grown, beds of two different styles are used, the flat beds supported by boards as described in the previous case, and the ridge beds, where the material, without any lateral support, is arranged in parallel ridges as shown in Fig. 225. This is the method largely, if not wholly employed in the celebrated mushroom caves at Paris, and is also used in some cases in the outdoor cultivation of mushrooms. As to the advantage of one system of bed over the other, one must consider the conditions involved. Some believe a larger crop of mushrooms is obtained where there is an opportunity, as in the ridge beds, for the mushrooms to appear on the sides as well as on the upper surface of the beds. In the flat beds the mushrooms can appear only at the upper surface, though occasionally single ones crop out in the crevice between the side board and the rock below.

THE HOUSE CULTURE OF MUSHROOMS.

Where this method of cultivation is employed, as the main issue, houses are constructed especially for the purpose. In general the houses are of two kinds. Those which are largely above the ground, and those where a greater or lesser pit is excavated so that the larger part of the house is below ground. Between these extremes all gradations exist. Probably it is easier to maintain an equable temperature when the house is largely below ground. Where it is largely above ground, however, the equability of the temperature can be controlled to a certain extent by the structure of the house. In some cases a wall air space is maintained around the sides and also over the roof of the building. And in some cases even a double air space of a foot or 18 inches each is maintained over the roof. In some cases, instead of an air space, the space is filled with sawdust, single on the sides of the house, and also a 12 or 18-inch space over the roof. The sides of the house are often banked with earth, or the walls are built of stone or brick.

The usual type of house is long and rather narrow, varying from 50 to 150 feet long by 18 to 21 or 24 feet wide. In some cases the single house is constructed upon these proportions, as shown by Fig. 226, with a gable roof. If it is desired to double the capacity of a house, two such houses are built parallel, the intercepting wall supporting the adjacent roof of the two houses, as shown in Fig. 227. A still further increase in the capacity of the house is often effected by increasing the number of these houses side by side. This results in a series of 8 or 10 houses forming one consolidated block of houses, each with its independent ridge roof and system of ventilation. The separating walls between the several houses of such a block are probably maintained for the purpose of better controlling the temperature conditions and ventilation in various houses. If desired, communication from one house to another can be had by doors.

Interior structure and position of the beds.—The beds are usually arranged in tiers, one above the other, though in some houses the beds are confined only to the floor space. Where they are arranged in tiers in a house of the proportions given above, there are three tiers of beds. There is one tier on either side, and a tier through the middle; the middle tier, on account of the peak of the roof at this point, has one more bed than the tiers on the side. The number of beds in a tier will depend on the height of the house. Usually the house is constructed of a height which permits three beds in the side tier and four in the center tier, with an alley on either side of the center tier of beds, giving communication to all. If the house is very long and it is desirable, for convenience in passing from one house to another, to have cross alley-ways, they can be arranged, but the fewer cross alleys the larger surface area there is for beds.

The size of the beds is governed by convenience in making the beds and handling the crop. The beds on the side tiers, therefore, are often three to three and one-half feet in width, affording a convenient reaching distance from the alley. The beds of the center tier have access from the alley on either side and are usually seven feet in width. The width of the alley varies according to the mind of the owner, from two to three or three and one-half feet. The narrow alley economizes space in the structure of a house; the wide alley, while slightly increasing the cost of the structure, makes it much more convenient in handling the material, and in moving about the house. The beds are constructed of one-inch boards. Various kinds of lumber are used, the hemlock spruce, the oak, Georgia pine, and so on. The beds are supported on framework constructed of upright scantling and cross stringers upon which the bottom boards are laid. These occur at intervals of three to four feet. The board on the side of each bed is 10 to 12 inches in width. The bottom bed, of course, is made on the ground. The upper beds in the tier are situated so that the distance is about three feet from the bottom of one bed to the bottom of the next above. Figs. 228 to 231 show the general structure of the beds.

Heating.—One portion of the house is set apart for the boiler room, where a small hot water heater is located. The position of the heater in one of these houses is shown in Fig. 227. In other cases, where the plant is quite a large one, a small separate or connecting boiler apartment is often constructed. In other cases, where the house is connected with or adjoining a system of greenhouses devoted to hothouse vegetables, the water pipes may run from the general boiler house which supplies the heat for all the houses. The water pipes in the mushroom houses are sometimes run beneath the boards or the walk in the alley, or in other cases are run just beneath the roof of the building.

Cultivation of mushrooms under benches in greenhouses.—This method is practiced to quite a large extent by some growers. In the house of Mr. William Swayne, Kennett Square, Pa., a number of large houses, devoted through the winter to the growing of carnations, are also used for the cultivation of mushrooms, a single long bed being made up underneath the beds of carnations. In these houses the water pipes providing heat for the building run along the sides of the building underneath the carnation beds at this point. Under these beds, where the water pipes run, no mushroom beds are made, since the heat would be too great, but under the three middle rows of beds in the house, mushroom beds are located. In this way, in a number of houses, several thousand square feet of surface for mushroom beds can be obtained. The carnations are grown, not in pots, but in a general bed on a bench. In watering the carnations, care is used in the distribution of the water, and in the amount used, to prevent a surplus of water dripping through on the mushrooms below.

Cellar culture.—For the cultivation of mushrooms on a small scale, unoccupied portions of cellars in a dwelling house are often used. The question is sometimes asked if it is injurious to the health of the family in a dwelling house when mushrooms are grown in the cellar. Probably where the materials used in making up the beds are thoroughly cured before being taken into the cellar, no injurious results would come from the cultivation of the plant there. In case the manure is cured in the cellar, that is, is there carried through the process of heating and fermentation in preparation for the beds, the odors arising from the fermenting material are very disagreeable to say the least, and probably are not at all beneficial to one's general health.

In the cellar culture of mushrooms the places selected are along the sides of the cellar in unused portions. Floor beds alone may be made by using the boards to support one side, while the wall forms the support on the other side as in the arrangement of beds on the side tiers in the mushroom houses; or tiers of beds may be arranged in the same way, one bed on the bottom, and one or two beds above. The number of beds will vary according to the available space. Sometimes, where it is not convenient to arrange the larger beds directly on the bottom of the cellar, or in tiers, boxes three or four feet, or larger, may be used in place of the beds. These can be put in out of the way places in the cellar. The use of boxes of this description would be very convenient in case it was desired to entirely do away with the possibility of odors during the fermentation of the manure, or in the making up of the bed. Even though the manure may be cured outside of the cellar, at the time it is made in the beds the odors released are sometimes considerable, and for several days might be annoying and disagreeable to the occupants of the dwelling, until such a time as the temperature of the manure had dropped to the point where the odors no longer were perceptible. In this case, with the use of boxes, the manure can be cured outside, made into beds in the boxes and taken into the cellar after the temperature is down to a point suitable for spawning, and very little odor will be released. If there is a furnace in the cellar it should be partitioned off from the portion devoted to mushroom culture.

Cultivation in sheds or out of the way places.—It is possible to grow mushrooms in a number of places not used for other purposes. In sheds where the beds may be well protected from the rain and from changing currents of air, they may be grown. In open sheds the beds could be covered with a board door, the sides of the bed being high enough to hold the door well above the mushrooms. In the basements of barns, or even in stables where room can be secured on one side for a bed, or tier of beds, they are often grown successfully.

Garden and field culture of mushrooms.—In Europe, in some cases, mushrooms are often grown in the garden, ridge beds being made up in the spring and spawned, and then covered with litter, or with some material similar to burlaps, to prevent the complete drying out of the surface of the beds. Sometimes they are cultivated along with garden crops. Field culture is also practiced to some extent. In the field culture rich and well drained pastures are selected, and spawned sometime during the month of May. The portions of spawn are inserted in the ground in little T-shaped openings made by two strokes of the spade. The spade is set into the ground once, lifted, and then inserted again so that this first slit is on one side of the middle of the spade and perpendicular to it. The spade is inserted here and then bent backwards partly so as to lift open the sod in the letter T. In this opening the block of spawn is inserted, then closed by pressure with the foot. The spawn is planted in this way at distances of 6 to 8 feet. It runs through the summer, and then in the autumn a good crop often appears.

CURING THE MANURE.

Selection of manure.—Horse manure is the material which is most generally used, though sometimes a small percentage of other manures, as sheep manure, is added. In the selection of the manure it is desirable to obtain that which is as fresh as possible, which has not passed through the stage of fermentation, and which contains some straw, usually as litter, but not too large a percentage of straw. Where there is a very large percentage of straw the manure is usually shaken out with a fork, and the coarser portion removed. If there is not too much of this coarse material the latter is often cured in a separate pile and used for the bottom of the beds, the finer portions of the manure, which have been separated, are used for the finishing and for the bulk of the bed.

Where manure is obtained on a large scale for the cultivation in houses or in caves, it is usually obtained by the carload from liveries in large cities. It is possible to contract for manure of certain livery stables so that it may be obtained in a practically fresh condition, and handled by the liverymen according to directions, which will keep it in the best possible condition for the purpose. In the cave culture of mushrooms the manure is usually taken directly into the caves, and cured in some portion of the cave. In the house cultivation of mushrooms there is usually a shed constructed with an opening on one or two sides, at the end of the house connected with the beds, where the manure may be cured. In curing it, it is placed in piles, the size of which will depend upon the amount of manure to be cured, and upon the method employed by the operator. The usual size, where considerable manure is used, is about three feet in depth by ten or twelve feet wide, and fifteen to twenty feet long. The manure is laid in these piles to heat, and is changed or turned whenever desirable to prevent the temperature from rising too high. The object of turning is to prevent the burning of the material, which results at high degrees of temperature in fermentation. It is usually turned when the temperature rises to about 130° F. At each turning the outside portions are brought to the center of the pile. The process is continued until the manure is well fermented and the temperature does not rise above 100 to 120 degrees, and then it is ready for making into beds.

There are several methods used in the process of curing, and it does not seem necessary that any one method should be strictly adhered to. The most important things to be observed are to prevent the temperature from rising too high during the process of fermentation, to secure a thorough fermentation, and to prevent the material from drying out, or burning, or becoming too wet. The way in which the material is piled influences the rapidity of fermentation, or the increase of temperature. Where the material is rather loosely piled it ferments more rapidly, and the temperature rises quickly. Watering the manure tends to increase the rapidity of fermentation and the elevation of the temperature. It is necessary, though, sometimes to water the material if the heat has reached such a point that it is becoming too dry, or if there is a tendency for it to burn. The material is then turned, and watered some, but care should be used not to make it too wet, since the spawn will not run in wet material.

In general we might speak of three different methods in the curing of the manure. First, the slow process of curing. According to this method, which is practiced by some, the time of fermentation may extend from four to five weeks. In this case the manure is piled in such a way that the temperature does not rise rapidly. During the four or five weeks the manure is turned four or five times. The turning occurs when the temperature has arisen to such a point as to require it.

Another method, used by some, might be called a rapid process of curing. According to this, the time for curing the manure extends over a period of about a week, or five to ten days. The material is piled in such a way as to cause rapid fermentation and rapid rising of temperature, the material sometimes requiring to be turned every day or two, sometimes twice a day, in order to lower the temperature and prevent the material from burning or drying out. Between this rapid process of curing, and the slow process of curing, the practice may extend so that, according to the method of different operators, the period of curing extends from one week to a month or five weeks.

The third method of curing consists in putting the material at once into the beds before curing, and mixing in with the manure, as it is placed in the bed, about one part of loam or garden soil to four or five parts of the fresh manure. The material is then left in this condition to cure without changing or turning, the temperature rising perhaps not above 130° F. With some experience in determining the firmness with which the bed should be made to prevent a too high rise of temperature, this practice might prove to be successful, and would certainly save considerable labor and expense in the making of the beds. Mr. William Swayne of Kennett Square, Pa., in the winter of 1900–1901, made up a portion of one of his beds in this way, and no difference could be seen in the results of the crop, the crop from the beds made in this way being as good as that of the adjoining beds, and he intends the following year to make up all of his beds in the same way.

Mixing soil with the manure at the time of fermentation.—While in the cave culture of mushrooms the manure is usually fermented and used without the admixture of soil, usually in the house or cellar culture rich loam soil, or rotted sod, is mixed with the manure at the time of turning it, during the process of fermentation. At the time of the first turning, soil is mixed in, a layer of the manure being spread out on the ground, and then a sprinkling of soil over this. Then another layer of the manure is added with another sprinkling of soil, and so on as the new pile is built up. In the first turning of the manure, about one part of soil is used to eight or nine parts of manure. Then at the last turning another mixture of soil is added, so that there is about one-fifth part soil in the mixture. The soil aids somewhat in lowering the temperature, and also adds some to the bulk, so that more beds can be made up with the same amount of manure.

Horse droppings free from straw.—For growing mushrooms on a small scale, as in cellars or boxes, some prefer to select the horse droppings free from straw.

MAKING UP THE BEDS.

Making up beds without the addition of soil.—In the cave culture of mushrooms the beds are usually made from manure alone, there being no addition of soil. This is perhaps partly due to the expense of getting the soil in and out from the caves as well as to the low temperature prevailing there. It is believed by many that the results are equally as good in beds from the manure alone as in those which contain an admixture of soil. The method of making the beds in the Akron cave, or "tunnel," is as follows: The manure, immediately after it has passed through the process of fermentation and curing in the pile, is carted to the district in the mine where the beds are to be made and is dumped in a long windrow on the ground. The length of the windrow depends of course upon the amount of material which is ready, as well as upon the amount necessary for making up the beds for that distance. Two hemlock boards, sixteen feet long and ten inches wide, and two, four feet long and the same width, are then hastily nailed into the form of a rectangular frame. This is placed upon the rock bottom at one end of the row of material, perpendicular to it usually.

The workmen then, with forks, distribute the material in this frame. If there is coarser material which has been separated from the finer material, this is placed in the bottom of the bed and the finer material is then filled on top. A layer of material is distributed over the bottom and then tamped down by striking with the back of the fork, as shown in Fig. 232. In this figure the material is shown to be off at one end of the bed. This was in a section of the mine where it was not convenient to follow the beds in the direction of the pile of manure, so that the material is distributed on from the end of the bed instead of from the side, as is the usual method. After several inches have been distributed in this way and tamped down with the back of the fork, the operator tramps over the material with his feet and presses it down more firmly. Another layer of material is distributed over this, and tamped and tramped down in a similar manner. The operation is repeated until the depth of the manure after tramping down is about seven inches. It is then left for the completion of the curing process and for the lowering of the temperature to the desired point. Usually, after making the bed in this way, there is a rise in the temperature for several days, gradually lowering until finally it reaches the point favorable for planting the spawn.

Where the beds are made successively, one after another, following the windrow of manure, the material used for the first bed removes from the windrow a sufficient amount to make room for the second bed, and in like manner room for the successive beds is provided for as the material is taken for each one, so that the frames are put together and the beds are formed rapidly and easily.

Making ridge beds in caves.—In the making of the ridge beds in caves there are two methods which might be spoken of. One method is the well known one practiced in certain of the caves near Paris, where the material is taken by workmen in large baskets and distributed in rows. The ridge is gradually formed into shape by walking astride of it, as additional material is emptied on from the baskets, the workmen packing and shaping the ridge by pressure from their limbs as they stand astride of the row. In this way the ridges are made as high or somewhat higher than their breadth at the base, and quite near together, so that there is just room in many cases to walk between the beds. In one cave in America, where the ridge system is used to some extent, the ridges are made with the aid of a board frame the length of the bed and the width of the base of the ridge. The long boards of this frame are slanting so that they are more or less the shape of the ridge, but not equal to its height. This frame is placed on the rock bottom, filled with manure and tramped on by the workmen. Then the frame is lifted on the ridge and more material is added and tramped on in like manner, until the bulk of the ridge bed is built up in this way and compressed into shape.

Beds in Houses Constructed for the Purpose of Growing Mushrooms.—Where only the floor of the house is used, a middle bed and two side beds are sometimes formed in the same manner as described in the construction of the house for the tiers of beds, with an alley on either side of the large center bed, giving access to all. In some cases the entire surface of the bottom is covered with material, but divided into sections of large beds by framework of boards, but with no alleys between. Access to these beds is obtained by placing planks on the top of the boards which make the frame, thus forming walks directly over portions of the bed. In some cases ridge beds, as described for cave cultivation, are made on the floor of these houses. The beds are filled in the same way as described for the cave culture of mushrooms, but usually, in the beds made in houses built for the purpose of growing mushrooms, a percentage of soil is mixed in with the manure, the soil being usually mixed in at the time of turning the manure during the process of fermentation. Garden soil or rich loam is added, say at the first time the manure is turned while it is fermenting. Then, some time later during the process of fermenting, another admixture of soil is added. The total amount of soil added is usually equal to about one-fifth of the bulk of the manure.

As this material, formed of the manure with an admixture of soil, is placed in the beds it is distributed much in the same manner as described for the making of flat beds in caves or tunnels. Usually, however, if there is coarse material which was separated from the manure at the first sorting, this without any mixture of soil is placed in the bottom of the bed, and then the manure and soil is used for the bulk of the bed above. This coarser material, however, is not always at hand, and in such cases the beds are built up from the bottom with the mixture of manure and soil. The depth of the material in the beds in these houses varies according to the experience of the operator. Some make the beds about eighteen inches in depth, while others do not make the beds more than eight or ten or twelve inches in depth. Where there are tiers of beds, that is, one bed above the other, very often the lowest bed, the one which rests directly upon the ground, is made deeper than the others.

While it is the general custom to use material consisting of an admixture of manure and soil in the proportions described, this custom is not always followed. In the case of the beds which are made up in the summer for the fall and early winter crop, soil, being easily obtained at that season of the year, is mixed with the manure. Some growers, however, in making the beds in midwinter for the spring crop, do not use any soil since it is more difficult to obtain it at that season. In such cases the beds are made up of manure alone. The experience in some cases shows that the crop resulting from this method is equally as good as that grown where soil has been added. In the experience of some other growers a bin of soil is collected during the summer or autumn which can be used in the winter for mixing in with the manure and making the beds for the spring crop. Where sod is used this is collected in pastures or fence rows in June, piled, and allowed to rot during the summer.

In distributing the material in the beds, the methods of packing it vary according to the wishes or experience of the grower. It is often recommended to pack the material very firmly. The feeling that this must be packed very thinly has led to the disuse of beds in tiers by some, because it is rather difficult to pack the material down very firmly where one bed lies so closely above another. Where the practice is followed of packing the material very firmly in the bed, some instrument in the form of a maul is used to tamp it down. Where there are tiers of beds an instrument of this kind cannot well be used. Here a brick or a similar heavy and small instrument is used in the hand, and the bed is thus pounded down firmly. This is a tedious and laborious operation. Many growers do not regard it as essential that the beds should be very firmly packed. In such cases the material is distributed on the beds and the successive layers are tamped down as firmly as can well be done with the back of a fork or an ordinary potato digger, which can be wielded with the two hands in between the beds. In the experience of these growers the results seem to be just as good as where the beds are more firmly packed down.

It is the practice in some cases where the bed lies against the side of the house to build up the material of the bed at the rear, that is, at the side of the house, much deeper than at the front, so that the depth of the bed at the back may be eighteen to twenty inches or two feet, while the front is eight to ten or twelve inches. This provides a slightly increased surface because of the obliquity of the upper surface of the bed, but it consumes probably a greater amount of material. It probably is not advantageous where the operations are carried on on a large scale, where abundant room is available, where the material for making the beds is expensive, and it is desirable to obtain from the material all that can be drawn in a single crop. The same practice is sometimes recommended and followed in the case of the beds made in cellars.

In the making of beds with fresh material, that is, with unfermented manure, as was done by Mr. William Swayne of Kennett Square, Pa., one season, the coarser material is put in the bottom of the bed, and then as the manure is distributed in the bed the soil is sprinkled on also, so that finally when the bed is completed the proportions of soil and manure are the same as when it is mixed in at the time of fermentation. In making the beds in this way, should any one be led to attempt it, it would be necessary to guard against a too high temperature in the fermentation of this fresh material; the temperature should not run above 130 degrees. It would also require a longer time from the making of the bed to planting the spawn than in the case of those beds where the manure is fermented and cured before being made up. Probably the total amount of time from the beginning to the completion of the preparation of the bed for spawning would not be greater, if it would be so great.

The beds all having been made, they are left until they are in a suitable condition for spawning. The determination of this point, that is, the point when the beds are ready for planting the spawn, seems to be one of the most important and critical features of the business. The material must be of a suitable temperature, preferably not above 90° F., and not below 70°. The most favorable temperature, according to some, other conditions being congenial, ranges from 80° to 85° F., while many prefer to spawn at 70° to 75°. Many of the very successful growers, however, do not lay so much stress upon the temperature of the bed for the time of spawning as they do upon the ripeness, or the cured condition, of the material in the bed. This is a matter which it is very difficult to describe to one not familiar with the subject, and it is one which it is very difficult to properly appreciate unless one has learned it by experience. Some judge more by the odor, or the "smell," as they say, of the manure. It must have lost the fresh manure "smell," or the "sour smell," and possess, as they say, a "sweet smell." Sometimes the odor is something like that of manure when spawn has partly run through it. It sometimes has a sweetish smell, or a smell suggestive of mushrooms even when no spawn has run through it.

Another important condition of the material is its state of dryness or moisture. It must not be too dry or the spawn will not run. In such cases there is not a sufficient amount of moisture to provide the water necessary for the growth of the mycelium. On the other hand, it must not be too wet, especially at the time of spawning and for a few weeks after. Some test the material for moisture in this way. Take a handful of the material and squeeze it. If on releasing the hold it falls to pieces, it is too dry. By squeezing a handful near the ear, if there is an indication of running water, even though no water may be expressed from the material, it is too wet. If on pressure of the material there is not that sense of the movement of water in it on holding it to the ear, and if on releasing the pressure of the hand the material remains in the form into which it has been squeezed, or expands slightly, it is considered to be in a proper condition so far as moisture is concerned for planting the spawn.

WHAT SPAWN IS.

The spawn of the mushroom is the popular word used in speaking of the mycelium of the mushroom. The term is commonly used in a commercial sense of material in which the mycelium is growing. This material is horse manure, or a mixture of one or two kinds of manure with some soil, and with the threads of the mycelium growing in it. The mycelium, as is well known, is the growing or vegetative part of the mushroom. Sometimes the word "fiber" is used by the mushroom growers in referring to the mycelium which appears in the spawn, or in the mushroom bed. The mycelium is that portion of the plant which, in the case of the wild varieties, grows in the soil, or in the leaf mold, in the tree trunk or other material from which the mushroom derives its food. The threads of mycelium, as we know, first originated from the spore of the mushroom. The spore germinates and produces delicate threads, which branch and increase by growth in extent, and form the mycelium. So the term spawn is rarely applied to the pure mycelium, but is applied to the substratum or material in which spawn is growing; that is, the substratum and mycelium together constitute the spawn.

Natural spawn or virgin spawn.—This is termed natural spawn because it occurs under natural conditions of environment. The original natural spawn was to be found in the fields. In the early history of mushroom culture the spawn from the pastures and meadows where mushrooms grew was one of the sources of the spawn used in planting. The earth containing the spawn underneath clumps of mushrooms was collected and used.

It occurs more abundantly, however, in piles of horse manure which have stood for some time in barn yards, or very often in stalls where the manure is allowed to accumulate, has been thoroughly tramped down and then has been left in this condition for some time. It occurs also in composts, hothouse beds, or wherever accumulations of horse manure are likely to occur, if other conditions are congenial. The origin of the natural spawn under these conditions of environment is probably accounted for in many cases by the presence of the spores which have been in the food eaten by the horse, have passed through the alimentary canal and are thus distributed through the dung.

The spores present in the food of the horse may be due to various conditions. Horses which go out to pasture are likely to take in with the food obtained in grazing the spores scattered around on the grass, and in the upper part of the sod, coming from mushrooms which grew in the field. In other cases, the spores may be present in the hay, having been carried by the wind from adjacent fields, if not from those which have grown in the meadow. In like manner they may be present in the oats which have been fed to the horse. In the case of stable-fed animals, the inoculation of the manure in this way may not always be certain or very free. But in the case of pasture-fed horses which are stalled at night probably the inoculation is very certain and very abundant, so that a large number of spores would be present in the manure from horses fed in this way.

The natural spawn also may originate from spores which are carried by the wind from the pasture or meadow mushrooms upon manure piles, or especially from spores which may lodge in the dust of the highways or street. Many of these spores would cling to the hoofs of the horses and at night, or at times of feeding, would be left with the manure in the stall. At other times horse droppings may be gathered from roads or streets where spores may be present in the dust. The piles of the droppings accumulated in this way, if left a sufficient time, may provide natural spawn by this accidental inoculation from the spores.

Probably few attempts have been made to grow the natural spawn with certainty in this country, though it does not appear to be an impracticable thing to do, since formerly this was one source of the virgin spawn in Europe. It is usually obtained by search through stables and barn yards or other places where piles of horse manure have accumulated and have remained for several months. In some cases the growers keep men employed through the summer season searching the yards and stables over a considerable area for the purpose of finding and gathering this natural spawn. It is probably termed virgin spawn because of its origin under these natural conditions, and never having been propagated artificially.

The natural spawn, as indicated above, is employed for a variety of purposes. It is used for inoculating the bricks in the manufacture of brick spawn. It is used for propagating once or twice in the mushroom beds, for the purpose of multiplying it, either in the manufacture of brick spawn, or for flake spawn, which is planted directly in the beds to be used for the crop. In some places in America it is collected on a large scale and relied on as the chief source of spawn for planting beds. In such cases the natural or virgin spawn is used directly and is of the first and most vigorous generation. It is believed by growers who employ it in this way that the results in the quality and quantity of the crop exceed those produced from the market spawn. But even these growers would not always depend on the natural spawn, for the reason, that collecting it under these conditions, the quantity is certain to vary from year to year. This is due probably to varying conditions of the season and also to the varying conditions which bring about the chance inoculation, or the accumulation of the material in the yard for a sufficient amount of time to provide the mycelium.

It would be interesting, and it might also prove to be profitable to growers, if some attempt were made to grow natural spawn under conditions which would perhaps more certainly produce a supply. This might be attempted in several different ways. Stall-fed horses might be fed a ripe mushroom every day or two. Or from the cap of ripe mushrooms the spores might be caught, then mixed with oats and fed to the horse. Again, the manure piles might be inoculated by spores caught from a number of mushrooms. Manure might also be collected during the summer months from the highways and aside from the probable natural inoculation which this material would probably have from the spores blown from the meadow and pasture mushrooms, additional inoculation might be made. The manure obtained in this way could be piled under sheds, packed down thoroughly, and not allowed to heat above 100° F. These piles could then be left for several months, care being used that the material should have the proper moisture content, not too dry nor too wet. This is given only as a suggestion and it is hoped that some practical grower will test it upon a small scale. In all cases the temperature should be kept low during the fermentation of these piles, else the spawn will be killed.

One of the methods of obtaining natural spawn recommended by Cuthill ("Treatise on the Cultivation of the Mushroom") is to collect horse droppings all along the highways during the summer, mixing it with some road sand and piling it in a dry shed. Here it is packed down firmly to prevent the heat rising too high. A "trial" stick is kept in the pile. When this is pulled out, if it is so hot as to "burn the hand," the heat is too great and would kill the spawn. In several months an abundance of the spawn is generated here.

Mill-track spawn.—"Mill-track" spawn originated from the spawn found in covered roadways at mills or along tram-car tracks where horses were used. The accumulation of manure trodden down in these places and sometimes mixed with sawdust or earth, provided a congenial place for the growth of the mycelium. The spawn was likely introduced here through spores taken in with the food of the horse, or brought there from highways, if they were not already in the soil from mushrooms grown there. It would be then multiplied by the growth of the spawn, and from spores of mushrooms which might appear and ripen. The well tramped material in which the mycelium grew here, when broken up, formed convenient blocks of spawn for storage and transportation, and probably led to the manufacture of brick spawn.

Manufactured spawn.—The manufactured spawn, on the other hand, is that which is propagated artificially by the special preparation of the substratum or material in which the mycelium is to grow. This material is inoculated either with a piece of natural spawn, or with pieces of previously manufactured spawn. It is put upon the market in two different forms; the brick spawn, and the flake spawn. The latter is sometimes known as the French spawn, while the former, being largely manufactured in England, is sometimes spoken of as the English spawn.

Figure 233.—Brick spawn. Three "bricks," one marked to show into how many pieces one brick may be broken.