288 BOTANICAL GAZETTE [ociober 



from the quite different form of its sporangia, as well as from the 

 absence of the peculiar tubercles which, according to Zopf, are 

 characteristic of that form. On the other hand, it is probable, 

 as has been suggested by von Minden (8) and Fischer (4), that 

 the sexual organs which Lindstedt found associated with his 

 D. polyspora, and on which he based the species, belonged in real- 

 ity to a member of some other genus which had accidentally been 

 introduced into his cultures. For this reason the species is per- 

 haps best regarded as in all probability invalid; and there thus 

 remain but two others, D. Magnusii Lindst. and D. monosporus 

 Leitg., with which the present form may be compared. On a 

 basis of sporangial characters alone it might readily be referred 

 to either of these species, and its failure to produce sexual organs 

 may be due to the fact that it is the antheridial strain of a uni- 

 sexual (dioecious) type, similar to that which both of the last 

 mentioned species are said to illustrate. On the other hand, it 

 may prove to be a neutral strain, comparable with Pieters' (9) 

 '^ Saprolegnia no. 66" and the undetermined species of Achlya 

 studied by the author (11), having lost its ability to reproduce 

 sexually, at least under ordinary conditions. That this may be 

 the correct explanation is further suggested by the fact that such 

 neutral or non-sexual conditions of Dictyuchus have previously 

 been reported by Humphrey (5), Tiesenhausen (10), and others; 

 while VON Minden even definitely identifies a form of this nature 

 with D. monosporus Leitg. Although it is quite possible that a 

 similar disposition of the present species might prove to be the 

 correct one, a definite specific reference does not seem justified at 

 the present time. 



In order to follow its development in detail, cultures which 

 were known to be uncontaminated by other forms were washed 

 repeatedly in sterile water and placed in a drop on a slide. As 

 soon as the zoospores had emerged, swarmed, and come to rest, 

 they were picked up with a capillary pipette, placed in a few 

 cubic centimeters of sterile water, and sprayed by means of an 

 atomizer on nutrient media contained in Petri dishes. The latter 

 were then examined under a low magnification, the positions of 

 single isolated spores were marked, and, after two or three days' 



