512 n. MARSHALL WARD. 



long branch from a neighbouring hypha, was in close contact 

 with the oogonium at 9 a.m., and the process of fertilisation 

 ■was already commenced, though no tube could be detected, 

 owing to the fatty globules of the egg coming close up to the 

 point of contact. At 12 noon, however, the contents of the 

 antheridium had passed over, the oospore was already 

 clothed with a membrane and its contents presented a dif- 

 ferent appearance, and the *'fertilising-tube" could now be 

 clearly seen extending between the oospore and the point of 

 attachment of the oogonium wall. The completely ripe 

 oospore (fig. 38) has a very thick membrane, and, in some 

 cases at least, a conspicuous central nucleus-like spot. 



It does not seem wise to attempt any further speculations as 

 to the relations of the three types of Pythium with which we 

 have been engaged; but it is clear that the one just described 

 cannot be included in P. gracile (De Bary). It is therefore 

 either the same as Schenk's P. gracile, with which it agrees 

 in habits, &c., or it is entirely new. This can only be decided 

 after the discovery of the zoosporangia. 



It now remains to describe all I was able to observe con- 

 cerning the fugitive Pythium, the zoosporangia of which 

 occurred mingled with those of P. gracile, as referred to on 

 p. 507, but which I could not cultivate separately. 



The zoosporangia (figs. 40 and 41) occurred as ovoid or 

 pyriform swellings of the ends of single, thin hyphse, which 

 projected vertically from the cress-seedlings, considerably over- 

 topping the sporangia of P. gracile (De Bary), with which 

 they were mingled. Each appeared in some respects similar to 

 those of P. proliferum already described, a resemblance 

 which might be insisted upon, if the mycelium of this form Avere 

 not so much more delicate, and if the zoosporangia were 

 developed upon racemose branchings, as in P. proliferum. 

 Such, however, was not the case, and I must regard this 

 slender form as distinct for the present. The development of 

 the sporange as a terminal swelling of the free hypha, which 

 then becomes separated off" by a septum and develops a beak as 

 a continuation of the long axis, are sufficiently shown in fig. 40, 



