OBSERVATIONS ON THE GENUS PYTHIUM. 503 



the empty membrane of the latter in the manner shown at fig. 

 18 — a not uncommon case. 



The oogonia and oospores of Pythium proliferum 

 were obtained in large quantities, and observed with ease ; 

 neither in the processes of development nor of fertilization did 

 I observe any facts of sufficient importance to need descrip- 

 tion, after what has been said concerning P. De Baryanum. 

 De Bary has pointed out that the antheridia are shorter and 

 less curved ; but whether the importance of the distinction can 

 be insisted upon I will not attempt to decide. The ripe oo- 

 spores also resemble those of P. De Baryanum very closely, 

 and need not be further described. Figs. 19, 20, and 21 show 

 the most important points. 



Pythium gracile (De Bary) 



may be selected as a further type, and I have had the op- 

 portunity to observe it closely. A form called P. gracile 

 had already been discovered by Schenk^ in the cells of Algee, 

 when De Bary found his P. reptans^ with similar habit; 

 both these species are either identical with Pringsheim's 

 P. monospernum^, or are so near that with the evidence at 

 command they cannot be definitely distinguished. For the 

 present, therefore, we must look upon De Bary's P. gracile Cri-^ 

 as possibly taking the place of these. It has been carefully 

 studied by De Bary^, and now stands as one of the best 

 known types of the genus. The general characters of P. gra- 

 cile are similar to those of the other forms, except that, as the 

 name implies, the hyphse are more slender ; correlatively, the 

 oospores and oogonia are more delicate than in the prece- _ , ,^\ 

 |\ ding forms. I obtained oospores from an old cultivation and ; 'Vf orlt 

 ') have depicted their structure and germination in fig. 22. The ^^*^1^ 



^f^^ '^^. > ' Verhaudl. d. Pliys. Med. Gesellsch.,' Wiirzburg, ix, 1857. '^ ^'' "' 



^'^ » 'Jahrb. f. wiss. Bot.,' ii, 1858. 



' ' Jahrb. f. wiss. Bot.,' i. 



* ' Bot. Zeit.,' Sept., 1881. De Bary, however, does not consider the 

 identity of these three forms settled. C. f. also 'Beitr. z. Morph. u. Pliys. d. 

 Pilze,' R. iv, 1881. See also below, p. 510. 



