Page:Popular Science Monthly Volume 26.djvu/633

 concentrated and protected, thus enabling the fungus to survive an exposure that might otherwise prove fatal. It should also be kept in mind that the substance of the leaf in which these spores are imbedded aids in shielding them from harm. If the vineyardist could destroy all these sexual spores at the end of the growing season, he would have little further trouble from the destructive mildew.

The members of the Cruciferæ, or cabbage family of plants, are quite generally attacked by white molds—so called because they cover the affected parts with a coating of almost pure white. A much magnified (four hundred times) view of the non-sexual spores is seen in Fig. 4. The white spores are produced in rows, forming below



and falling away from the top, in the simplest possible manner. The contents of the spores divide in germination as in the grape-mildew above described. A ruptured spore is shown one thousand times magnified, in the lower right-hand corner of the figure, while the ciliated protoplasmic bodies (zoöspores) are seen above. These white molds are provided with sexual winter spores very similar to those described for the grape-mildew; in fact, the two groups are closely related, and belong to the same family of fungi. Fig. 5 shows the mature sexual spores of Cystopus candidus, magnified four hundred diameters, one of which has its hard shell ruptured and its contents of zoospores escaping. It requires weeks and even months for the development of these sexual spores, and frequently a long time may elapse before germination takes place. On this account they have received the very appropriate name of resting-spores. They remain within the tissue of the plant, and are frequently liberated only by its decay. The life of the white molds passes over from one season to another in these rough, thick-coated spheres of protoplasm, the formation of which approaches in complexity that of the seeds of higher plants.