Probably there are not many farmers who use a microscope and fewer still who use one to help them in their business, yet there are few people to whom one of these instruments would be more useful. Their seeds are often far from pure and the microscope will reveal the impurities which may consist of dirt and dust, or of other seeds, seeds which will grow into weeds and make the crop less valuable or, if present in large quantities, render it valueless. Agricultural plants become attacked by varied diseases which can only be studied under the microscope; insects also do their share of destruction and much may be learned about them when they are magnified. Fungi and insects not only attack crops but domestic animals as well. The microscope is an invaluable aid in studying the soil, in dairy work and in many other ways closely connected with agriculture.

That the testing of agricultural seeds is very important is shown by the fact that not very long ago a deputation urged the Government to establish a National Seed Testing Station; no further plans have been made, however. Seed testing is very interesting work, every seed has its particular shape and markings and the student soon becomes absorbed in seeking for weed seeds among the collections he examines. A weed in the sense we use it here is not necessarily a harmful plant, it is a plant in the wrong place. For example a carrot growing in a field of turnips, though a useful plant would be a weed. When the farmer sowed turnip seed he did not do so with the object of raising carrots.

The only apparatus necessary for the study of most farm seeds is a powerful magnifying glass, one that will enlarge the seeds ten diameters or more. When beginning this work, a difficulty occurs at once for, without assistance from an expert, it is by no means easy to learn the names of the seeds one examines. The difficulty can be overcome to a certain extent if we know the names of flowers, for then we can collect the seeds from these flowers and we shall have properly named specimens as a guide. Beginning in this way, we shall soon find that the seeds can be arranged in groups and there will then be no difficulty in recognising say clover seed or grass seed, though much more experience will be necessary before we can say to which kind of clover or grass the seed belongs.

Many of these seeds are well worth studying, whether we are interested in seed testing or not. The corn buttercup and the wild carrot have curious spined seeds; those of the larkspur when magnified appear to be studded with little shreds of paper. White and red campion, have kidney shaped seeds studded with warts and so similar to one another that the microscopist who can distinguish one from the other may consider himself something of an expert. Spurrey has lens shaped seeds with raised equator-like rims. Evening primrose seeds are curious because they are found in all sorts of shapes. The seeds of rib-wort plantain resemble miniature date seeds, others resemble minute bananas, some are perfectly round, others almost square; some have smooth shining surfaces which look as though they had been artificially polished, others again are wrinkled and deeply furrowed; but, most curious of all the common seeds are those of the cornflower, they resemble nothing so much as little shaving-brushes, with bright yellow bristles. Many profitable hours may be spent in studying the seeds of our common native plants, both wild and cultivated.

There are two specially obnoxious plants whose seeds may be mixed with agricultural seed, to the dismay of the farmer. We refer to Broomrape and Dodder, both of them unable to earn their own living and depending for their existence on the robbing of other plants. Broomrape usually attaches itself to the roots of Hazel, Poplar or Beech and steals its food therefrom, but its fleshy pink stems and flowers may sometimes be seen in clover fields, then clover is its victim.

More common and more destructive is the little Dodder, a member of the Convolvulus family. Its seeds are very minute and when they germinate they give rise to a seedling not unlike a piece of wire. With one end fixed in the ground, the other waves about till it finds a clover plant round which it twines and not only so but it sends out suckers which microscopic examination shows, penetrate the stem of the clover to rob its food. By pulling a Dodder stem away from the clover we can clearly see a number of holes where the suckers have entered.

Fungus diseases and insects wage constant warfare on the farmer’s belongings. That we may better understand the structure of the disease-causing fungi we are about to examine, let us refresh our memories concerning that very common fungus, known as white mould and mentioned in an earlier chapter. The reason fungi cause damage to other plants, the one invariable reason, is that they, being unable to manufacture food for themselves, steal it from the plants on which they grow. Some of them are parasites and steal their food from living animals or plants; others live upon dead animal or vegetable matter and the white mould is one of the latter fungi.

In most of the fungi which concern us we shall find that there is a mass of minute, thread-like structures forming the main body of the fungus and that, here and there, portions grow erect and bear spores. The spores, it is important to remember, serve the same purpose to the fungus as seeds to the flowering plants. They are blown or carried by insects or other agencies to suitable situations for growth, they germinate and form new fungi. They are smaller and lighter than the most minute and dust-like seeds, so that the slightest breeze scatters them far and wide. Let us compare the white mould with a mushroom; at first sight the two plants appear very dissimilar, in reality they are very similar to one another. The mould forms a thick felt of its threads over the substance on which it grows and mushroom spawn if carefully examined under a microscope will be found to consist of very similar threads, sealed together to form thicker root-like structures. The fungi, however, have no roots and these threads are strictly comparable with those of the mould. Here and there the mould sends a single thread into the air and each of these threads is terminated by a little ball which bursts eventually and sets free its contained spores. The same thing occurs with the mushroom; we have the upright growth, not of a single thread it is true but of a number, welded together to form a fleshy stalk; at the top there is, not a ball containing spores but an umbrella-shaped structure whose under surface is composed of a number of “gills” on which the spores grow at the ends of little stalks. If a piece of the mushroom stem be torn into its separate components and examined under the microscope, its similarity to the more simple fungus is evident. One of the gills also may be carefully cut away and examined; the spores will be seen at the end of small forked stalks.

Having progressed thus far in our study of fungus structure, we may examine a few of those which cause damage in farm and garden. For the most part, the thread-like portion of the fungus grows within the plant attacked and only the spore bearing portions appear on the surface. There is one class of fungus, however, the Mildews in which practically all the structure grows on the surface, only a few small, unbranched suckers penetrate the plant attacked, for the purpose of obtaining nourishment.

Though of great interest to the microscopist, the potato disease is often the cause of serious loss to the farmer. Not only potatoes but also tomatoes are attacked. A potato plant suffering from the disease has irregular yellowish or brownish spots upon its leaves in the summertime. An examination of the lower surface of one of these spotted leaves will reveal a silvery white margin to each spot. This portion should be magnified with a fairly high power and care must be taken not to injure the diseased part of the leaf before it is examined. In cases of serious disease, from nearly every pore on the surface of the leaf fungus threads will be seen to issue. The threads are branched and, at the end of each branch, they have a special kind of spore. They look not unlike miniature leafless trees and they give the typical silvery white appearance to the margins of the diseased spots. When the spores of potato disease germinate, the young fungus threads enter the leaf through a pore and for sometime afterwards there is no sign that the plant is diseased. On this account potato disease and many other fungus diseases are rendered more serious in that the farmer is not and cannot be aware that his crop is attacked till the disease has taken a firm hold. Eventually the potatoes themselves become brown, rotten and breeding grounds for bacteria.

A very common plant disease which makes a good study for the microscope, may be found in quantity upon shepherd’s purse, and as it also attacks cultivated plants of the same family, cabbages, cauliflowers and the like, it is of no little importance. In its early stages, the fungus looks like patches of thick white paint upon the plant and where the fungus grows the plant is invariably contorted. As the fungus matures, the skin of the diseased plant splits and a white powder issues. If some of this powder be highly magnified, it will be found to consist of chains of spores, six or seven in a chain. The spores break off singly and each one may start the disease in another plant.

The microscopist who hunts in garden and farm for fungus diseases, will assuredly meet with some examples of that large class known as “smuts.” They are so called on account of the black powder with which the attacked portions of the plants become filled. The smuts are very important but are not of much interest as objects for the microscope, so we will pass them over for subjects of greater interest if of less importance.

Every farmer knows the familiar and destructive fungus known as “rust of wheat,” it is one of a large class of most interesting plants. The “rusts” are interesting to the microscopist on account of their structure and to the botanist because they cannot, like other fungi, complete their lives upon one plant. They derive their popular name from the fact that they look like patches of rust upon the plants on which they live. Some of the greatest living agricultural botanists have spent many years on producing races of wheat upon which rust fungus will not grow. Wonderful success has rewarded their efforts and conferred immense benefits upon farmers. In spite of this, however, we need not despair that we shall be unable to find a specimen for our microscope, though it is happily an undoubted fact that the disease is not so common now as a few years ago.

Rust of wheat fungus grows part of its time on barberry leaves and part on wheat. In the summer, if we examine one of the rust-like patches on stem or leaf of wheat we shall see that it consists of a dense bunch of small, short stalks each one of which is terminated by an oblong red-brown spore. If we keep another patch of the fungus under observation, we shall find as the season advances, that instead of the red-brown patch it has grown darker and darker till it has become almost black. The microscope will show us that the structure of the spores has altered considerably. There is still the same bunch of stalks but they have lengthened somewhat and now each spore which terminates each stalk is divided into two parts by a wall across its narrow part. The walls surrounding the spores also appear thicker, as indeed they are. These are the winter spores, they fall to the ground eventually and there they remain, unharmed by frost or snow or rain, till the spring. In the spring they germinate and give rise, not immediately to another fungus, as might be expected, but to another kind of spore. Curiously enough these new spring-formed spores cannot grow upon wheat and unless they are carried by wind or some other agency to a barberry plant their existence is ended. Should they reach a barberry leaf, however, they will germinate, penetrate the leaf and grow for a period. Eventually the fungus appears on the lower surface of the leaf in beautiful structures called cluster cups. Under the microscope, one of these cluster cups forms a lovely object. The leaf skin is split and below the ruptured skin may be seen a flask-shaped hollow filled with chains of minute golden-yellow spores. The spores break away, one by one and favoured by fortune, are carried to a wheat plant where they germinate and give rise to the familiar rust. Any microscopist anxious for research has a life’s work before him in tracing the histories of this one class of fungi, should he feel inclined to shoulder the burden. Very many cluster cups are known and very many rusts and all that is required is an enthusiastic mycologist, as the student of fungi is called, to put the pieces of the puzzle together, so to speak. It is not so very many years ago that the connection between the cluster cups of barberry and the rust of wheat was quite unthought of.

We cannot afford much more space to plant diseases, the farmer has other troubles and we must mention some of them. We cannot leave the subject, however, without a word concerning the mildews. As we have mentioned, they are curious because they dwell outside the plants they attack. Rose mildew is unfortunately all too common in every garden, it may be recognised as a white powder covering leaves and buds. Under the microscope, in the summer we shall find that it consists of a number of thread-like structures, not unlike those of the common white mould and that there are a number of erect chains of spores. Towards autumn, a further examination will show us many round dark-brown structures from which project a number of minute threads. These brown spheres are the winter stage of the fungus, designed to withstand inclement weather. In the spring, the spheres burst and set free a number of minute sacs, each one containing eight spores. The spores germinate on rose leaves and start the disease anew.

There will be no difficulty in finding mildews; they are all very similar to the rose mildew in general but they all differ in detail. The gooseberry mildew for example, has a large number of threads running from its winter spheres and each thread is terminated by a little group of branches. The sacs which fall from the opened sphere in the spring, only contain four spores in this case.

The animal enemies of the farmer, so far as they concern the microscopist are more difficult to study. Many of them are internal parasites and to gain a real knowledge of their habits and life histories necessitates a good deal of rather unpleasant work for which the ordinary microscopist has neither the time nor the inclination.

In order to give our readers some idea of this work, let us take one of the commonest of all agricultural parasites and trace its life history whilst giving hints for its examination under the microscope. The common liver fluke is a worm which, in the adult stage, frequents the liver of some domestic animal, usually the sheep. A friendly butcher will probably be able to supply us with a specimen and, when we receive it, we shall probably dub it a very unwormlike creature. The worms form a large class in the animal kingdom and they do not all resemble the earthworm by any manner of means.

The liver fluke is a flat, almost leaf-like creature, it is not ringed like the earthworm and, under the microscope, we can plainly see all its internal organs. The fluke lays its eggs, each one enclosed in a little capsule, in the liver of the sheep. They are carried to the intestines and finally set free along with the animal’s excrement. If then the eggs are blown, or carried by some means to water they will continue their development, on dry soil they cannot long survive. Each egg gives rise to a little organism which swims freely in the water; it is shaded like a blunt-ended cone when extended and is roughly oval when contracted. Its body is covered with little whip-like structures similar to those of the slipper animalculÆ, and it is due to the lashing of these little whips that the creature moves through the water. If we found one of these young flukes in some pond water we might be forgiven for thinking it to be some near relative of the slipper animalcule. When our subject finds a living water snail it enters its breathing organs, becomes affixed to their walls and loses its covering of little whips. It becomes transformed into a shapeless mass which later develops into an elongated structure, quite unlike the free swimming creature which took shelter within the snail. Next, a migration is made to the liver of the snail where birth is given to, from fifteen to twenty, curious little heart-shaped organisms each with a tail about twice as long as its body. These little creatures escape from the snail and swim freely in the water for a time. Eventually they make their way to herbage growing by the waterside, affix themselves thereto and become surrounded with a hard coat capable of resisting the effects of hot sun or drying winds. Should this herbage be eaten by cattle, the apparently lifeless young fluke bestirs itself, loses its tail and wends its way to the liver of its host, then the story begins again.

Having examined the adult liver fluke under the microscope, we shall probably wish to find both the free swimming young forms, and if we search carefully in ponds to which sheep have access we are likely to be rewarded. It is obvious that the life of a parasite such as the liver fluke is, of necessity, precarious. It is only chance or luck, or whatever one’s favourite term may be, that brings the egg to water, the young fluke to a snail, and the last free swimming form to herbage that will be eaten by a suitable animal. As usual in such cases, nature makes provision for emergencies by providing a large number of young, in order to insure that some at least may be able to complete their development. Owing to a series of changes, which we have omitted to describe for the sake of simplicity, each liver fluke egg may give rise to no less than three hundred and twenty of the final free swimming forms.

As we have remarked, the study of parasites is difficult but it is interesting. Very few of these creatures can complete their lives without living at the expense of two different animals. The liver fluke needs the water snail and some herb-feeding animal; there is another parasite which spends part of its life in the pig and another part in the grub of the cockchafer; a third parasite dwells for a time within the thrush, and for the rest of its time within the garden snail, and so on. Apart from the interest of the subject in itself, it brings us face to face with the fact that many quite unrelated forms of animal life are essential to the well being of a number of parasites. To the farmer the subject is all important.

Insects of various kinds are all important in agriculture; most of them are harmful, some few are useful. They have, however, been dealt with in another chapter, so we will dismiss them here. The ticks are closely related, and anyone with access to a farm should be able to obtain some specimens. Whatever species we are able to obtain should be examined under the microscope. Their feet are always interesting, being furnished with powerful claws beautifully adapted to grasping the hairy coats of their hosts. Their mouth parts are quite unlike those of insects, and are always furnished with a number of backwardly directed teeth, which are useful for tearing flesh sufficiently to draw blood on which they feed.