PHYCOMYCETES.—CYSTOPUS. 379 
ridia (fig. 835, B, an), are formed by branches which arise from 
near the base of the oogonium. In the course of its develop- 
ment, the oogoniwm becomes of a more or less spherical form, 
and at its base a septum is formed separating it from the general 
cavity of the Cystopus mycelium, whilst the greater part of the 
protoplasm contained in the oogonium arranges itself so as to 
form a rounded inass known as the oosplere (jig. 835, B, 0s). 
Fic. 835. 
Fig. 835. A. Branched mycelium of Cystopus with young oogonia, 0g, og. 
B. Portion of mycelium bearing oogonium, og, with the oosphere, os; 
and antheridium, an. c. Mature oogonium, with os, the oospore. D. 
Mature oospore. £, F. Formation of swarm-spores or zoospores, G, from 
the oospores. i, i. Protruded endospore. After De Bary. 
When fertilisation is about to take place, one or other of the 
antheridia comes in contact with the oogonium (jig. 835, B, an), 
and subsequently the protoplasm of the antheridium reaches 
that of the oogonium by penetrating the membrane of the latter 
(fig. 825, B). An oospore is thus formed (fig. 835, C, 0s), which 
becomes surrounded by a rough dark brown coat or exospore, 
and contains numerous starch granules (fig. 835, pD). After 
lying dormant during the winter, the protoplasm of the oospore 
becomes divided into numerous segments, the whole being 
covered bya thin membrane known as the endospore (fig. 835 B, 
i, and F, 1); and from each of the little segments of protoplasm 
is formed a zoospore or swarm-spore (fig. 835, G). The endospore 
ultimately forces itself like a bladder (fig. 835, E, 7, F, 7) through 
the exospore, and then bursting, the zoospores, G, are set free, 
