Page:Popular Science Monthly Volume 26.djvu/631

 description arc popularly considered as very transient, and as frequently lasting for only a day. They start from a simple body called a spore, produce a network of fine threads, yield a crop of spores in a few hours, and the cycle of life is completed. We, however, find that this round of multiplication is varied, and even these evanescent mildews produce structures which serve the special purpose of carrying the species over trying times of starvation, drought, or cold. The common bread-mold (Mucor stolonifer), for example, so abundant upon stale viands in warm, moist weather, forms spore-bearing capsules upon the tips of perpendicular threads, which, when ripe, burst, and the multitudes of minute spores are scattered in all directions by every passing breeze. As the bread begins to get dry, and fails to yield a full supply of nourishment, the mold commences to develop a second form of spore. These are produced by the union of the contents of two filaments (conjugation), as shown in Fig. 1. The two Indian-club-shaped branches are touching, end to end, at a and b; the union is



more advanced at c, while at d a central cell has formed, containing the mingled contents of the two united cells. At e is seen the mature spore, which has a thick, hard, black, and spiny covering, well adapted to protect its highly vitalized contents from all injury. This spore, though magnified ninety times in the engraving, is very much larger than the exceedingly minute sacs of protoplasm formed in the capsules above mentioned. The latter germinate at once, when favorably situated, but the larger black spore remains dormant for a considerable time. Rapid reproduction is provided for in the multitudes of small summer spores, while the preservation of the species is the end sought in the formation of the thick-coated black spores.

Passing from the minute molds that thrive upon bread, cake, etc., we come next to those parasitic species of fungi growing in the tissues of higher forms of plants. The grape-mildew (Peronospora viticola)