294 BOTANICAL GAZETTE [October 



the genus; but in view of the detailed investigations of Leitgeb 

 and others it seems doubtful if such is the case. It must be 

 admitted, however, that Saprolegnia had been studied for many 

 years before Leitgeb observed in it the diplanetism on which he 

 based his genus " Biplanes. " On the other hand, the repeated 

 zoospore emergence in the present instance might be regarded as 

 peculiar to this particular and perhaps hitherto unnoticed species 

 of Dictyuchus. Since such an assumption is contrary to our cus- 

 tomary conception of the fixity of generic characteristics, its truth 

 may well be doubted. In view of the tardy recognition of the 

 extent of this phenomenon in the genus Pytkium, it is possible 

 that it has merely been overlooked in the recognized species of 

 Dictyuchus. Finally, it is possible that this phenomenon occurs, 

 not only in various species of Dictyuchus, but also in other genera 

 of the Saprolegniaceae under certain favorable conditions; and 

 that these conditions either have not been attained in cultures 

 heretofore, or the emergence has escaped observation. It seems 

 highly probable that this is the case, and that in certain Sapro- 

 legniaceae there inheres in the protoplasm, even of encysted 

 zoospores of the second type, the abiHty to form not only germ 

 tubes but also zoospores; and that under proper circumstances 

 the latter may be produced. Probably, then, as Atkinson (i) 

 has suggested in the case of Pythium, this repeated zoospore 

 emergence may best be regarded as a phenomenon of germination, 

 and one which the author believes can be brought about by cer- 

 tain favorable conditions. It is possible that extensive cultural 

 studies of various Saprolegniaceae, with this end in view, will 

 demonstrate that its occurrence is far more widespread than has 

 been suspected. The writer is obliged to admit, however, that 

 he has been unsuccessful in many attempts to induce repeated 

 zoospore emergence in Achlya and Thraustotheca; but the well 

 known sensitiveness of the Saprolegniaceae to surrounding condi- 

 tions makes it possible that these failures may have been the 

 result of faulty methods. 



In any case, the occurrence of this phenomenon in even a 

 single species of Dictyuchus points to the conclusion that the 

 customary application of such terms as " monoplanetic " and "di- 



