1 84 



MORPHOLOG Y. 



them more distinct by treatment with Schultz's solution, draw- 

 ing 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. 



395. Sexual reproduction of saprolegnia. When such cultures are older 

 we often see large rounded bodies either at the end of a thread, or of a 

 branch, which contain several smaller rounded bodies as shown in fig. 196. 

 These are the oogonia (unless the plant is attacked by a parasite), and the 

 *round bodies inside are the egg cells, if before fertilization, or the eggs, if 

 after this process has taken place. Sometimes the slender antheridium can 

 be seen coiled partly around the oogonium, and one end entering to come in 

 contact with the egg cell. But in some species the antheridium is not 

 present, and that is the case with the species figured at 196. In this case 



B 



Fig. 202. Fig. 203. 



Gonidiophores and gonidia of potato blight (Phytophthora in- Gonidia of potato 



festans). i, an older stage showing how the branch enlarges where bjight forming zoogo- 



it grows beyond the older gonidium. (After de Bary.) nidia. (.After de Bary.) 



the eggs mature without fertilization. This maturity of the egg without 

 fertilization is called parthenogenesis, which occurs in other plants also, but 

 is a rather rare phenomenon. 



396. In fig. 199 is shown the oogonium and an antheridium, and the 

 antheridium is carrying in the male nucleus to the egg cell. Spermatozoids 

 are not developed here, but a nucleus in the antheridium reaches the egg 

 cell. It sinks in the protoplasm of the egg, comes in contact wi'h the nu- 

 cleus of the egg, and fuses with it. Thus, fertilization is accomplished. 



