But there must have been a long antecedent time, when the lowest fungi were non-parasitic, and grew upon the moist warm ground as Botrytis terrestris, Pers., sometimes does now. In those far-off times the primordial plant was probably a mere microscopic cell or thin sac resting on the moist surface of the earth, as illustrated at A, Fig. 141. It probably increased by division, as at B, and redivision, as at C; each of the four parts soon becoming distinct, as at D, and each segment speedily reaching the original size and form, as at E. Or it might have increased by budding, like yeast. From this simple beginning many observers believe it probable that all plants have been developed. The primal cell might have been a fungus, an alga, or a form occupying an intermediate position between fungi and algæ, as both fungi and algæ may have originated from a primal and at present unknown stock CHAPTER XXXVIII. CONCLUSION. WE have now rapidly passed in review some of the most familiar forms of disease as seen in our field and garden crops, and not a few of our readers may possibly think the details as described both complicated and difficult. Yet on careful study it will be found that the courses of all diseases more or less follow one or two simple general plans. The details may vary and the colours may be changed, but the chief outlines are not essentially different from each other. It is only in the knowledge obtained after completely mastering the life history of each disease that any preventive remedy against disease can be hoped for. With a full knowledge of the character and habit of an enemy, it can be fought under favourable circumstances, as in a bright light. Without the proper knowledge it is like fighting against a powerful, unknown, and merciless foe in the dark. One point that must impress every reader is the extreme, almost inconceivable, smallness and attenuation of the parts of some of the most destructive of our field and garden fungi. To give an idea of this smallness, we have in Fig. 142 engraved the foot of a common housefly, with its hairs and claws, enlarged 100 diameters. At AA are seen six of the spores or conidia of the potato fungus, Peronospora infestans, Mont. Each of these spores contains within itself, on an average, eight other little spores or zoospores, illustrated as free from the investing spore or conidium at B, and each of these smaller spores has two inconceivably fine cilia or vibrating hairs, by which it can propel and guide itself over any moist surface. The large spores of the putrefactive fungus of lettuces, Peronospora Schleideniana, Ung., are shown at C ; others of the putrefactive fungus of clover P. exigua, Foot of house-fly, with the spores of various parasitic fungi. W.Sm., at D; and the spores of the smut fungus of grain, Ustilago carbo, Tul., at E. Every one who has walked amongst potato plants must have noticed the small green fly or plant-louse, Rhopalosiphum dianthi, Schrank, shown, the natural size, at B, Fig. 143. Some of the female lice possess wings, as shown, Ꮓ but so small and gauzy that they may be readily overlooked. One of these small and inconceivably thin wings is shown enlarged to 20 diameters at Fig. 143, X 20 FIG. 143. Green fly, from potato plant, natural size, and wing with spores or conidia of the potato fungus, Peronospora infestans, Mont., at A. Enlarged 20 diameters. and on the wing at A, engraved to the same scale, are a number of conidia or spores of the potato fungus. Small as these germs are as seen on the greatly enlarged wing, yet each atom under favourable circumstances encloses no less than eight other atoms, each furnished with two vibrating hairs, and endowed with the power of sailing rapidly about in any non-corrosive film of moisture. It need hardly be said that various insects and flies, both large and small, commonly eat or imbibe fungus spores. The spores are not only to be seen dusted over the wings or sticking amongst the hairs of the legs, but they are quite as commonly seen inside the insects as out; this is especially well seen in such small transparent insects as plant-lice or aphides. The spores are carried about with the juices inside the bodies of the insects, and may not only be found in the body, but inside the limbs, and even within the almost invisible antennæ or horns. The spores of various fungi not only stick to the bodies of insects, but they germinate upon them and produce mycelium outside, and sometimes, inside their bodies. Mr. G. B. Buckton, F.R.S., in commenting upon our observations on this subject in his Monograph of British Aphides, says the facts need cause no surprise. Small as some of these organisms or parts of organisms may be, it must not be assumed that we are acquainted with the smallest objects of nature. On the contrary, every new and true observation about minute things indicates that what we already know regarding small things is as nothing when compared with what is not known, and what at present we seem to have but little prospect of knowing. The most perfect and powerful telescopes cannot resolve the more distant nebulæ into stars, neither can the most perfect microscopes display to our sight numerous atoms which are believed to exist, but which cannot be seen. Persons possessed of strong vision can often see, both with the telescope and microscope, objects that are invisible to persons of ordinary sight. It would be very rash, therefore, for any observer to say that certain objects or characters do not exist simply because that observer cannot see them. Neither |