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BOTANY 



PART II 



In Olpidiopsis, which is parasitic in the hyphae of Saprolegnia, the method of 

 conjugation is different and more like that of the higher Phycomycetes. Larger 

 female and smaller male protoplasts lie side by side in the host cells, where they 

 grow, become multinucleate, and surround themselves with cell walls. The 

 contents of the male cell now pass into the female cell, which becomes a thick- 

 walled oospore. The nuclei appear to fuse in pairs. The further fate of this 

 oospore is not known. Olpidiopsis also multiplies by biciliate zoospores formed 

 in sporangia. 



In other genera no sexuality has yet been demonstrated and no conjugation 

 precedes the development of the resting sporangia. 



Order 2. Oomycetes 



1. Only in the small primitive family of the Monoblepharideae ( 54 ) are free 

 ciliated spermatozoids liberated from the antheridia. In the other Oomycetes the 



FIG. 370. Monoblepharis sphaerica. End of filament with terminal oogonium (o) and an antheridium 

 a). 1, Before the formation of the egg-cells and spermatozoids. % t Spermatozoids (s) escaping 

 and approaching the opening of the oogonium. 3, osp, ripe oospore, and an empty antheridium. 

 (x 800. After CORNU.) 



multinucleate contents of the antheridium do not divide into separate spermatozoids. 



The species of Monoblepharis live in water upon decaying remains of plants. 

 Asexual reproduction is effected by means of uniciliate swarm-spores, formed in 

 large numbers in sporangia. The oogonium, which is usually terminal, contains 

 only a single egg-cell (Fig. 370). 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 ( 55 ), which connect on to the preceding family, live like 

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

 living fishes. Asexual propagation is effected by club-shaped sporangia (Fig. 371) 

 which produce numerous biciliate swarm-spores. In Saprolegnia these swarm-spores 

 with terminal cilia withdraw the latter and become surrounded with a spherical 

 wall ; shortly afterwards, the contents again escape as bean-shaped zoospores 

 with the cilia inserted laterally. The sexual organs develop on older branches of 



