IV 



PKZIZALHS 



10: 



oogonium, from which a trichogyne protruded (fig. 61 />). The union of the 



trichogyne and antheridium was observed and it was shown that from the 



oogonium ascogenous hyphae subsequently 



arose. Van Tieghem recorded that the species 



is very susceptible to external conditions, the 



antheridium sometimes being reduced in size 



or absent, though the oogonium nevertheless 



developed normally and produced ascogenous 



hyphae. 



In 1900 appeared the classical researches 

 of Harper, followed in 1903 and 1907 by 

 Dangeard's, and in 1912 by Claussen's investi- 

 gations. 



The mycelium is made up of cells of varying 

 length, regularly multinucleate, containing six 

 to twelve nuclei, and filled with cytoplasm of 

 a loose, spongy structure. The mycelium is 

 sparse and loose, but the reproductive organs 

 are very abundant so that the ascocarps, when 

 mature, are often crowded together. 



The first indication of sexual reproduction 

 consists in the appearance of thick hyphae, 

 very similar to the corresponding filaments in 

 Ascodesmis, and tending, like them, to stand 

 at right angles to the substratum. They dicho- 

 tomize (fig. 61 a), the terminal cells become swollen, and two types, the more 

 spherical oogonium and the more elongated antheridium, are distinguished; 

 these arise on separate branches, but from the same mycelium. Both are 

 multinucleate from their initiation. 



Very soon a slight elevation appears on the oogonium; it elongates 

 rapidly to form the multinucleate trichogyne and, before its growth is 

 complete, is separated from the oogonium by a wall; the trichogyne and 

 antheridium grow towards one another, the tip of the trichogyne meeting 

 sometimes the apex, but more commonly the flank of the male organ. 



The mature oogonium is a spherical or flask-shaped cell filled with 

 dense-cytoplasm and containing many nuclei which are very much larger 

 than those of the ordinary vegetative cells. Its stalk consists of two or 

 three broad cells, its apex is continued into the trichogyne. The nuclei of 

 the latter increase but little in size and are thus much smaller than those of 

 the essential organs at maturity. The nuclei of the antheridium are almost 

 as large as those of the female cell, but its protoplasm is less dense owing 

 perhaps to the absence of accumulated reserve materials. It would appear 



Fig. 61. Pyronema con/luens Tul.; a. 

 development of sexual apparatus; 

 b. mature oogonia ami antheridia ; 

 x 390; after de Bary. 



