=392. Appearance of the saprolegnia.=—In the course of a few days we are quite certain to see in some of the cultures delicate whitish threads, radiating outward from the body of the fly in the water. A few threads should be examined from day to day to determine the stage of the fungus. [Illustration: Fig. 195. Sporangia of saprolegnia, one showing the escape of the zoogonidia.] =393. Sporangia of saprolegnia.=—The sporangia of saprolegnia can be easily detected because they are much stouter than the ordinary threads of the mycelium. Some of the threads should be mounted in fresh water. Search for some of those which show that the protoplasm is divided up into a great number of small areas, as shown in fig. 195. With the low power we should watch some of the older appearing ones, and if after a few minutes they do not open, other preparations should be made. [Illustration: Fig. 196. Branch of saprolegnia showing oogonia with oospores, eggs matured parthenogenetically.] [Illustration: Fig. 197. Downy mildew of grape (Plasmopora viticola), showing tuft of gonidiophores bearing gonidia, also intercellular mycelium. (After Millardet.)] [Illustration: Fig. 198. Phytophthora infestans showing peculiar branches; gonidia below.] =394. Zoogonidia of saprolegnia.=—The sporangium opens at the end, and the zoogonidia swirl out and swim around for a short time, when they come to rest. With a good magnifying power the two cilia on the end may be seen, or we may make them more distinct by treatment with Schultz’s solution, drawing some under the cover glass. The zoogonidium is oval and the cilia are at the pointed end. After they have been at rest for some time they often slip out of the thin wall, and swim again, this time with the two cilia on the side, and then the zoogonidium is this time more or less bean-shaped or reniform. [Illustration: Fig. 199. Fertilization in saprolegnia, tube of antheridium carrying in the nucleus of the sperm cell to the egg. In the right-hand figure a smaller sperm nucleus is about to fuse with the nucleus of the egg. (After Humphrey and Trow.)] [Illustration: Fig. 200. Branching hypha of Peronospora alsinearum.] [Illustration: Fig. 201. Branched hypha of downy mildew of grape showing peculiar branching (Plasmopara viticola).]