80 



MANUAL OF BOTANY 



In C^'stopus {fig. 832) the germination takes the form of the 

 production of a number of zoospores, which are set free. In 

 Pythium and other genera it results in the production of a small 

 promycelium, which in time gives rise to spores. 



The Saprolegnise all live in water, being parasitic in some 

 cases, though often saprophytic. The Salmon disease is due to 

 one species of this group. The gonidangia are here club-shaped 

 and give rise to zoospores {fig. 834). The sexual organs are 



Fig. 832. A. Brauclicd mycelium of Cus/opiis, with young oogonia, oj, og. 

 B. Portion of mycelium bearing oogonium, oy, with the oosphere, oi ; and 

 autheridium or poUinodium, an. c. Mature oogonium, with os, the 

 oospore. D. Mature oospore. E, F. Formation of swarm-spores or zoo- 

 spores, G, from the oospores, i, i. Protruded endospore. After De Bary. 



similarly produced to those of the last group, but the oogonium 

 contains usually several oospheres {fig. 833). In their formation 

 there is no periplasm left. The pollinodia usually send tubes 

 into the oogonium, but there is no passage of the male gamete. 

 The oospheres become oospores without fusion with the latter, 

 that is parthenogenetically. 



In the Oomycetes, as in the Zygomycetes, antithetic alterna- 

 tion of generations occurs, but the sporophyte is always small and 

 inconspicuous. It is represented by the oospore itself in such 



