PERONOSPORALES 1021 



After a rest period the oospore germinates. l In the course of this 

 process, in Pythium angustatum for example, the large oil globule 

 disassociates into a number of refractive parts (Fig. 84 F, p. 1018) that 

 become regularly dispersed throughout the now evenly and finely 

 granular protoplasm. Coincidently with these changes, the oospore wall 

 steadily decreases in thickness, apparently being absorbed by the 

 protoplasm (Fig. 84 G). The germ hypha, now somewhat constricted 

 as it pierces the spore wall, elongates, branches, and establishes the 

 new mycelium (Fig. 84 H). In water, certain of its branches may be 

 converted into sporangia. Only vegetative development takes place in 

 nutrient solutions. 



In Pythiogeton sex organs are presumably formed, but absolute proof 

 is as yet lacking. This uncertainty appears largely due to failure of sex 

 organs to develop in pure culture and to the inability of the observer 

 to trace assuredly in gross culture the connection between the sexual 

 and the nonsexual phases. Minden (1916) found two somewhat similar 

 types of sex organs in his material, one of which he associated with P. 

 utriforme (Fig. 88 H, p. 1045) and the other with P. transversum (Fig. 88 

 D). The one he assigned to the former species had been previously 

 observed by Thaxter (1895b) growing with Gonapodya, which frequently 

 occurs in the same habitat as Pythiogeton. It has since been recorded by 

 other investigators, for example, Lund (1934), and Sparrow (1936a). By 

 the two workers mentioned, it was seen, as in Minden's cultures, in 

 conjunction with sporangia of P. utriforme. The type which Minden 

 associated with P. transversum, has evidently not been reported since his 

 time. The two types of sex organs Minden allied with the sporangial 

 stages of P. utriforme and P. transversum are here recognized as valid 

 until evidence to the contrary is forthcoming. 



According to Minden (1916), in Pythiogeton utriforme the rudiments 

 of the antheridia and the oogonia arise as two small vesicles of about 

 equal size, in contact with one another and, at least in some plants, on 

 the same hypha. One of these swellings, the antheridium, which frequent- 

 ly is subterminal on its supporting hypha, fails to grow larger, whereas 

 the other, the oogonial rudiment, expands and becomes packed with 

 spherical or angular refractive structures. During development of the 



1 See Drechsler's (1955) account of this process in P. butleri. 



