Page:Popular Science Monthly Volume 9.djvu/425

Rh a diameter much greater than that of the filaments which have produced it, and is many hundred times the size of the spores formed in the capsules. It is also provided with two coats, the outer one thick, dark-colored, and covered with warty excrescences, except on the two ends where the remnants of the conjugated filaments remain. Successive stages in the development of these spores are shown in Fig. 3. At a the two swollen threads are near each other; b, the process partly completed, with the middle cell plainly seen; and c, the full-formed zygaspore, with the remains of the old cells. The importance of these sexual spores in the economy of the plant is not difficult to



understand. The minute asexual spores have a very thin covering, and under favorable conditions will germinate as soon as formed, but on the other hand are readily destroyed by extreme climatic changes. The large, well-protected zygospores which germinate only after months of ripening, are in every way fitted to carry the species through the unpropitious season of winter, times of drought, and severe exposure. When the zygaspore germinates it produces very soon a large crop of capsules, and their little spores are scattered far and wide ready to develop into plants in a few hours, as circumstances shall decide. This dual form of fruiting is an interesting feature in the life of these little plants, and is as effectual in preserving the species as it is interesting.

After upward of a week from the time the Mucor, of which we have been speaking, made its appearance on the bread, another mould was noticed growing-over its surface, which was of a much finer structure and dingy yellow in color. When placed under the microscope, it was found to be peculiar, both in structure and habit of growth. The filament which bears the spores, as it rises from the matted surface of the Mucor, divides into two branches, each of these into two others, and so on, until ten or more branches are reached. The same angle of divergence being preserved in all the branching, the