380 



BOTANY 



single egg-cell (Fig. 315). The antheridia, which resemble the sporangia, liberate 

 a number of uniciliate spermatozoids. On a spermatozoid reaching the egg-cell 

 through an opening in the tip of the oogonium an oospore is formed. A spinous 

 cell wall forms around the oospore. 



2. The Saprolegniaceae ( 52 ), which connect on to the preceding family, live like 

 them saprophytically on the surface of decaying plants and insects ami even on 

 living fishes. Asexual propaga- 

 tion is effected by club-shaped . 

 sporangia (Fig. 316) which pro- 

 duce numerous biciliate swarm - 



spores. The sexual organs develop Q 



on older branches of the mycelium 

 (Fig. 317 a). The oogonia give 

 rise to a larger (as many as 50) 

 or smaller number of egg-cells, 

 rarely only to a single one. At 

 first the egg-cell contains numer- 



FlO. 816. Saprolegnia miita. 

 biciliate zoospores, s 2 , are es 

 from the sporangium. 



The 



Fio. 317. Saprolegnia mixta. Hyphre bearing 

 the sexual organs ; o, antheridium which has 

 sent a fertilisation tube into the oogonium ; o', 

 egg-cell ; o", oospore enclosed in a cell-wall ; op, 

 parthogenetic oospores ; g, young oogonium. 

 (After G. KLEBS.) 



ous nuclei, but usually all but the single nucleus of the egg degenerate. The 

 tubular, multinucleate antheridia apply themselves to the oogonia and send 

 fertilising tubes to the egg-cells. One male nucleus enters the egg-cell and 

 fuses with its nucleus (Fig. 318). The oospore after fertilisation acquires a 

 thick wall. In some forms belonging to this family and to the Peronosporeae 

 the formation of antheridia is occasionally or constantly suppressed ; the oospores 

 develop parthenogenetically without being fertilised (Fig. 317). 



3. The Chytridiaceae ( M ) are microscopically small Fungi parasitic on aquatic or 



