Elementary botany . nt with Schultzs solution, draw-ing some under the cover glass. The zoogonidium is oval andthe cilia are at the pointed end. After they have been at restfor some time they often slip out of the thin wall, and swimagain, this time with the two cilia on the side, and then thezoogonidium is this time more or less bean-shaped or reniform. 395. Sexual reproduction of saprolegnia.—When such cultures are olderwe often see large rounded bodies either at the end of a thread, or of abranch, which contain several smaller rounded bodies as shown in fig. are the oogonia (unles
Elementary botany . nt with Schultzs solution, draw-ing some under the cover glass. The zoogonidium is oval andthe cilia are at the pointed end. After they have been at restfor some time they often slip out of the thin wall, and swimagain, this time with the two cilia on the side, and then thezoogonidium is this time more or less bean-shaped or reniform. 395. Sexual reproduction of saprolegnia.—When such cultures are olderwe often see large rounded bodies either at the end of a thread, or of abranch, which contain several smaller rounded bodies as shown in fig. are the oogonia (unless the plant is attacked by a parasite), and theround bodies inside are the egg cells, if before fertilization, or the eggs, ifafter this process has taken place. Sometimes the slender antheridium canbe seen coiled partly around the oogonium, and one end entering to come incontact with the egg cell. But in some species the antheridium is notpresent, and that is the case with the species figured at 196. In this case. Fig. 202. Fig. 203. Gonidiophores and gonidia of potato blight (Phytophthora in- Gonidia of potato festans). b, an older stage showing how the branch enlarges where blight 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 withoutfertilization is called parthenogenesis, which occurs in other plants also, butis a rather rare phenomenon. 396. In fig. 199 is shown the oogonium and an antheridium, and theantheridium is carrying in the male nucleus to the egg cell. Spermatozoidsare not developed here, but a nucleus in the antheridium reaches the eggcell. It sinks in the protoplasm of the egg, comes in contact with the nu-cleus of the egg, and fuses with it. Thus fertilization is accomplished. FUNGI: DOWNY MILDEWS. I85 Downy Mildews. 397. The downy mildews make up a group of plants which are closelyrelated to the water moulds, but they are parasitic on land plants, an
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