The term larger fungus refers to any fungus whose study does not necessarily require more than a low-powered lens to see most of the important morphological features. Using such a term cuts across the existing scientific classification, for it includes the more obvious fungi bearing their spores on specialised reproductive cells called basidia, fig. 5, and a few of those whose spores are produced inside specialised reproductive cells called asci. The term is useful, however, even though it embraces a whole host of unrelated groups of fungi; it includes the polypores, fairy-clubs, hedgehog-fungi, puff-balls and elf-cups, as well as the more familiar mushrooms and toadstools—or puddockstools as they are often called in Scotland. Specimens of all these groups will find their way some time into the collecting baskets of the naturalist when he is out fungus-picking, along with probably a few jelly-fungi and less frequently one or two species of the rather more distantly related group, the morels. The biggest proportion of the finds, however, on any one collecting day in the autumn, when the larger fungi are in their greatest numbers, will be of the mushrooms and toadstools; these are, collectively, more correctly called the agarics.

The early botanists and pioneer mycologists of the nineteenth century recognised the fact that the fungi both large and small are ecologically connected to the herbaceous plants and trees among which they grow, but many mycologists since have tended to neglect these early observations. Although the importance of the fungi in the economy of the woodland, copse, field and marsh is well-known, mycologists and ecologists alike have been rather slow to appreciate that the fungi can be just as good indicators of soil conditions, if not better, than many other plants. Perhaps it is rash to attempt such a treatment as you find here because we know so little of the reasons why a particular fungus prefers one habitat to another. However, it is envisaged and hoped that, if a framework is provided, accurate field-notes can gradually be accumulated and many of the secrets yet to be uncovered explained.

Where to look

Fungi can be found in most situations which are damp at some time of the year. Searching for fungi can begin as soon as the spring days become warm, although even in the colder periods of winter several finds can be made. In summer it gets very dry and this necessitates collecting in damper areas, such as marshes, alder-carrs, swamps and moorland bogs. After a heavy storm in summer, on the edges of paths and roadsides, woodland banks, in clearings in woods and in gardens, fungi can be collected within a few days of the rain, but collecting normally reaches a climax in August-September, the precise date depending on the locality and the individual character of the particular year.

All woodlands are worth visiting, particularly well-established woods with a mixture of trees. Pure pine-woods do not seem to be as good as pine-woods with scattered birch; plantations are often disappointing except after heavy rain or late in the season, even well into November in mild years. Pure birch and beech, the latter particularly when on chalky soils, are excellent areas to visit. Oak is possibly not as good but areas with willow and alder have many unique species. The edge of woods, sides of paths or clearings are usually more productive areas to search in than is the depth of the wood, and a small plot of trees can be much more rewarding than a large expanse of woodland. After some time one is able to judge the sort of place which will yield fungi. Rotten and burnt wood are very suitable substrates for they retain the moisture necessary for growth of fungi even in dry conditions, so allowing fructification to take place.

Grasslands including hill-pastures, established sand-dunes, etc., are often excellent, but of course they are much more dependent on the weather to produce favourable conditions for fungal development than woodland areas where the changes in the humidity and temperature are less extreme; prolonged mist or mild showery weather favour the fruiting of the grassland fungi. Dung in both woods and fields is an excellent although ephemeral substrate; many species of fungi characterise dung whilst others will grow in manured fields, on straw-heaps or where man has distributed the habitat.

Collecting

The collecting of larger fungi should not be considered a haphazard pursuit; careless collecting often results in many frustrating hours being spent on the identification of inadequate material, which is also not suitable after for preservation as reference material. A few good specimens are infinitely better than several poor ones; one is always tempted to collect too much and then collections are inevitably discarded. Always try to select specimens showing all the possible stages of development from the smallest buttons to the expanded caps. Sometimes such a range is not possible and one must be satisfied with either a couple or only one fruit-body.

Carefully dig up or cut from the substrate the entire fungus and handle it as little as possible. A strong pen-knife or fern-trowel is admirable for the job. The associated plants should be noted, especially trees, and if one is unable to identify the plants or woody debris retain a leaf or a piece of wood for later identification. One should note in a field-notebook any features which strike one as of interest, such as smell, colour, changes on bruising, presence of a hairy or viscid surface.

For transporting home the specimens should be placed in tubes, tins or waxed paper which are themselves kept in a basket. The smallest specimen can go in the first, the intermediate-sized forms in the tins or waxed paper and the larger ones laid in the basket or placed in large paper bags; plastic bags are not suitable except for very woody fungi. Thus an assortment of tins, tubes and various sizes of pieces of waxed paper are essential before setting out on a collecting trip. The specimens should be placed in the waxed paper such that they can be wrapped once or twice and the ends twisted as if wrapping a sweet.

Examination

Once home always aim at examining the specimens methodically.

The first necessity is to determine whether the fungus, which has been collected, has its spores borne inside a specialised reproductive cell (ascus) i.e. Ascomycete, or on a reproductive cell (basidium) i.e. Basidiomycete. By taking a small piece of the spore-bearing tissue, mounting in water, gently tapping it and examining under a low power of the microscope this can be easily ascertained. The tapping out is best done with the clean eraser of a rubber-topped pencil. There are several different shaped asci and basidia; the latter structures are more important in our study because the Ascomycetes are in the main composed of microscopic members.

The following procedure is necessary for the examination of your find:—

Select a mature cap of an agaric from each collection, cut off the stem and set the cap gills down on white paper, or if the specimen is small or is a woody or toothed fungus, or consists of a club or flattened irregular plate, place the spore-bearing surface (hymenium) face down on a microscope glass slide. The smaller specimens must be placed in tins with a drop of water on the cap to prevent drying out. Even with the larger specimens it is desirable to place a glass slide somewhere under the cap between the gills and the paper, and if possible to enclose the species carefully in waxed paper or in a tin. Whilst you are waiting for the spore-print to form, notes must be made on the more easily observable features; one is not required at this stage to examine the microscopic characters.

All the characters which may change on drying must be noted immediately, and these include colour, stickiness, shape, smell and texture. A sketch, preferably in colour, however rough, can give much more information than many score words.

Cut one fruit-body, longitudinally down with a razor or scalpel or a sharp knife if the fruit-body is woody, and sketch the cut surfaces, fig. 1A-B. These sketches and the rest of the collection notes should be made such that identification and future comparisons can be achieved. Thus always note the characters in the same order for each description. A table of the important characters is provided here, but this is meant as a guide not as a questionnaire. The attachment of the gills, pores or teeth to the fruit-bodies when once the fungus is in section should be always noted (see p. 20).

The spore-print when complete should be allowed to dry under normal conditions and then the spore-mass scraped together into a small pile. A microscope cover-slip should be placed on the top of the pile and lightly pressed down. The colour of the spore-print (or deposit) can then be compared with a standard colour chart and the spores making up the print examined in water under a microscope.

Microscopic examination

When one is more experienced with fungi it will be found necessary to carry out many microscopic observations, but when commencing the study it is necessary only to have an ordinary microscope; a calibrated eyepiece-micrometer is an advantage as is an oil-immersion lens. An examination of the spores is always necessary; the examination of features such as the sterile cells on the gill and stem, etc., varies with the fungus under observation. Spores should if at all possible be taken from a spore-print and mounted on a microscope slide, either in water or in a dilute aqueous solution of household ammonia. Although for mycologists it is often necessary to measure spores to within a ¹/₂ micron (µm) this book has been so arranged that one only really has to distinguish between a spore which is small (up to 5 µm), medium (5-10 µm), long (10-15 µm), or large if globose and very long (if over 15 µm); this is not strictly accurate, but serves the purpose for an introductory text. It is important to describe the character of the spore, i.e. ornamentations, whether a hole (germ-pore) is present at one end and/or a beak (apiculus) at the other (fig. 5). With white or pale coloured spores it is useful to stain either the spore or the surrounding liquid with a dye—10% cotton blue solution is admirable, or a solution of 1·5 g iodine in 100 ml of an aqueous mixture containing 5 g of potassium iodine and 100 g of chloral hydrate. Both these dyes must be accurately made up if the study of the fungi is to be taken at all seriously; because some of the chemicals used above are not normally required by students, a chemist must make up the reagents for you. Often the spores turn entirely or partially blue-black or pale blue or purplish red in the iodine solution—a useful character.

Material in good condition is always required and one of the first things the student needs to do is train himself to collect sufficient material in good condition. The steps by which all the structures of the fungus used in the text can be observed are outlined below:—

Fig. 1 shows the cuts required to furnish suitable sections in order to observe the various structures and patterns of tissue which are important.

1. Carefully place the longitudinal section (AB) of the fruit-body which has been sketched gill-face down under a low power or dissecting microscope. Hairs or gluten on the cap, if present, will be made visible by focusing up and down (figs. 2 and 3A) and/or those on the stem (fig. 3B). When any part of the cut fruit-body is not being examined retain it in a chamber containing damp paper or moist moss; this will assist the cells to retain their turgidity, for they frequently collapse on drying and are difficult to observe except after performing often lengthy and special techniques.

If only one fruit-body is available, then cut along CD and mount in a tin box on a slide in order to obtain a spore-print (otherwise see paragraph 6).

2. Cut off a complete gill (E) and quickly mount on a dry slide. Under the low power of a microscope, the cystidia on the gill-margin will be visible (fig. 4); it will be seen whether the spores are arranged in a particular pattern (fig. 5) and whether the basidia are 2-spored or 4-spored. In white-spored toadstools it is difficult sometimes to determine whether the basidia are 2- or 4-spored so one must confirm the observations by other techniques.

A section of the gill accompanied by a small piece of cap-tissue, as in E, will confirm the presence or absence of noticeable cystidia (or hairs) on the cap. Now mount the section bounded by FG and HI in a drop of water containing either a drop of washing-up liquid and/or glycerine; the soapy liquid helps to expel any water which may tend to cling to the gill-margin amongst the cystidia and the glycerine stops the mount from drying out whilst further sections for comparison are cut and examined. It is at this time that the structure of the outermost layer of the cap can be examined, e.g. whether it is made up of a turf-like structure; the presence or absence of cystidia on the cap can be also confirmed (fig. 7A-C). It is frequently necessary to tap the mount in order to spread the tissue slightly and expose the elements; this can be done very efficiently by light pressure from the end of a pencil to which an eraser is attached. Cut off along line JK to eliminate marginal cystidia from confusing the picture and mount both pieces separately.

3. Cut out a wedge of tissue from the fruit-body (L) so as to have several gills attached to some cap-tissue; until one is familiar with the variability of facial and marginal cystidia, carefully cut along the line PQ (note: the cut is made one-third of the distance from the cap margin, thus eliminating the possibility of large numbers of marginal cystidia being examined in error for facial cystidia). Now make a second cut along the line of RS so that finally a small block of tissue remains (M).

Mount on a dry slide with the plane through PQ face down on the slide and observe under a low magnification, to assess whether cystidia on the gill-face are present or absent, and if present their general shape and whether numerous or infrequent (fig. 8).

Mount in water/washing-up mixture as outlined above and tap gently with the rubber attached to the end of a pencil; evenly distributed pressure should be given. If the gills appear to be too close then rotate the rubber a little whilst pressing in order to spread the tissue.

4. Using a low power of a microscope and looking down into the plane RS of the unmodified block M or a similar block, one obtains by this simple technique a very accurate idea as to the structure of the trama of the gill (fig. 9). The organisation of this tissue is very important in classification, some groups of toadstools having what has been described as regular trama (fig. 9C), others irregular (fig. 9D), inverse (fig. 9B) or divergent (fig. 9A). This same tissue may be thick or sparse to wanting, coloured or not. Such sections are often better than attempts at very thin sections unless very specialised techniques are used. There are few satisfactory thicknesses between the two extremes; the thick sections you can do and the very thin requiring expert techniques.

5. Take out a small block of tissue T as indicated in the figure (fig. 1). Mount immediately and repeat as in 3. This will allow the outer layer of the cap to be more clearly seen (fig. 7A-C) and also the structure of the flesh (fig. 10). The latter may be composed of a mixture of filaments and ‘packets’ or ‘nests’ of rounded cells (i.e. heteromerous), or of filaments, only some of which may be inflated (i.e. homoiomerous); but when individual cells are swollen they never form distinct groups. By very similar techniques it is possible to show that the more woody fungi can have flesh composed of one of four types of cells (Corner, 1932): these types depend on whether distinctly thickened cells (plate 47) are present with the actively growing hyphae or not (pp. 140-150), whether hyphae are present which bind groups of hyphae together, etc. (plate 46).

6. Remove stem along line CD and cut out small blocks of tissue as indicated (U, V and W). Mount immediately and examine as in paragraph 3, for cystidia, etc. (see fig. 3).

Whilst all these sections are being cut and processed a second fruit-body, if available, should be set to drop spores; this is done by cutting off the cap from the stem and placing it either entirely or in part, and with gill-edges down, on a slide in a tin.

7. Z is a ‘scalp’ of a cap; a thin sliver from the cap is placed on a slide in a drop of water (modified with washing-up liquid, etc. as above). After placing a cover-slip over the tissue it is tapped gently; this will show if the cap is composed of globose to elliptic elements or if it is composed of strictly filamentous units (figs. 6A & B). Care must be taken not to reverse the section when transferring it to the mountant, either by turning the scalpel or by allowing the surface tension of the liquid to pull the section upside down. The construction of any veil fragments will also be seen in this mount, and if a loose covering of veil is present this should be removed before observation so that it does not obscure the fundamental structures.

8. Examine the stipe of the fruit-body used above under a low power or with a dissecting microscope in order to ascertain whether there are any remains of veil and/or vegetative mycelium. If found, mount immediately in the solution containing iodine mentioned above and examine.

Of course it is difficult to carry out the above system the first time and be successful in seeing everything, indeed in being able to cut all the sections 1-8. Practice makes perfect, so why not practise with a ¹/₄ lb of mushrooms from the grocer before the autumn season starts. In this way you will have overcome the difficulties without having to experiment with your collections.