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INTRODUCTION TO THE STUDY OF FUNGI 



place, by the concentration of the denser portion in the centre, 

 in the form of a sphere, involved in a delicate membrane, 

 surrounded by a hyaline layer of protoplasm. At this time 

 the antheridium is being developed from a lateral branch of 

 the hypha, just below the oogonium (Fig. 107). When fully 

 developed this organ is elliptical or obovate, smaller than the 

 oogonium, and filled with granular protoplasm ; cut off at the 

 base from connection with the hypha by a transverse septum. 

 Assuming that the oosphere is formed, and the antheridium 

 perfected, the latter comes in contact with the former, and, at 

 the point of contact a slender tube is projected through the wall 

 of the oogonium, which grows until it reaches the surface of the 



Fig. 107. — Peronospora. a, young state ; b, formation of oosphere ; 

 c, after fertilisation. After De Bary. 



oosphere. Meanwhile the contents of the antheridium under- 

 go change : towards the centre they are more dense, and, as the 

 fertilisation tube becomes complete, this portion passes down 

 it and mingles with the protoplasm of the oosphere, and the 

 connection is complete. The oosphere is fertilised, and, secret- 

 ing a thick wall, becomes an oospore, a resting spore, analogous 

 to the zygospore of the Mucoraceae. Gradually, by the decay 

 and dissolution of the hyphae, these oospores become free, 

 hybernating amidst the decaying tissue of the foster-plant, 

 and awaiting rejuvenescence in the spring. When the latter 

 period arrives the contents of the oospore, in most species, 

 become differentiated into a host of minute active zoospores, 

 similar to those evolved from the differentiated gonidia, and, 

 by rupture of the wall of the mother cell, become diffused and 

 ready to attach and establish themselves upon young seedlings 



