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.
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.
Fig. 196.
Branch of saprolegnia showing oogonia with
oospores, eggs matured parthenogenetically.
Fig. 197.
Downy mildew of grape (Plasmopora viticola),
showing tuft of gonidiophores bearing gonidia,
also intercellular mycelium. (After Millardet.)
Fig. 198.
Phytophthora infestans showing
peculiar branches; gonidia below.