1020 AQUATIC PHYCOMYCETES 



single hypha from which they usually arise often surrounding the female 

 gametangium in P. adhaerens (Fig. 84 A, p. 1018). When fully mature 

 each antheridium is delimited from the hypha by a cross wall, formed 

 generally at about 15 u. from its tip, which is in contact with the oogonial 

 wall (Fig. 84 B). Fertilization is accomplished in from three to five 

 hours by the gradual transference of all, or nearly all, of the antheridial 

 contents to the oogonium through a cylindrical refractive tube, about 

 2 [i. in diameter, which penetrates the wall of the oogonium and extends 

 an unknown distance into the ooplasm (Fig. 84 C). 



Coincidently with the formation of the fertilization tube, the contents 

 of the oogonium become more condensed and contract away from the 

 wall (Fig. 84 C). The ooplasm, connected by hyaline strands of proto- 

 plasm to the oogonial wall, generally lies in an eccentric position, in close 

 contact with the part of the wall penetrated by the fertilization tube. 

 During fertilization the contents, instead of having a smooth densely 

 granular consistency, become darker and extremely irregular in contour. 

 As the discharge of antheridial material progresses, the ooplasm contin- 

 ues to contract and the fine droplets of oil which are distributed through- 

 out it combine to form large, irregularly shaped, highly refractive bodies, 

 which finally compose nearly the whole mass. 



After fertilization, the contour of the oospore becomes more even, 

 the refractive bodies rapidly decrease in size, and the protoplasm 

 assumes a coarsely granular aspect. No periplasm could be observed 

 in living material. 1 There is now formed around the ooplasm a thin 

 pellicle which gradually thickens. Finally, during the formation of 

 the wall, the oil droplets dispersed throughout the somewhat mottled 

 oogonial protoplasm fuse into a large centrally disposed refractive 

 globule, whose diameter is usually about one third that of the oospore 

 (Fig. 84 D-E, p. 1018). Between the inner face of the wall and the oil 

 globule a lenticular structure, probably a nucleus, appears. The mature 

 oospore in this species lies loosely within the oogonial wall (Fig. 86 I, 

 p. 1030); that is, it is "aplerotic" (in the sense of Middleton, 1943) in 

 contrast to "plerotic" or completely filling the oogonium (Fig. 86 J). 



1 According to Patterson (1927), periplasm in Pythium torulosum was difficult to 

 demonstrate even by cytological methods. On the other hand, it was relatively con- 

 spicuous in living material of P. dictyosporum (Sparrow, 1931a). 



