48 THE SAPROLEGNIACEAE 



single oogonium, often only one present. Oospores up to 15 and 20 

 in an oogonium, average diameter 24 microns, with rather thick walls." 



Pieters (1. c.) found that in two collections, one from Germany 

 and one from Ann Arbor that he considered S. mixta, there were an- 

 theridia, usually of diclinous origin, on at least 90% of theoogonia; the 

 mycelium being flaccid and delicate, the pits while present less promi- 

 nent than in S. ferax. These characters are suspiciously like our 5. 

 delica and it seems to us rather likely that Pieters had that species 

 and not S. mixta as here considered. We cannot think that S. delica is 

 deBary's 5. mixta, as he emphasizes the close resemblance of the latter 

 to S. ferax and 5. monoica, and they are very different from 5. delica. 

 Particularly is this true in regard to the oogonia, which are thin-walled 

 and with few and inconspicuous pits in the latter, while in the Ferax 

 group the walls are thicker and with far more abundant and conspicuous 

 pits. Most conspicuously is this true for S. ferax, a.nd deBary says that 

 the oogonial structure of 5. mixta is most like that of S. ferax, with the 

 pits often A-ery large. This would never do for 5. delica. Moreover, 

 the often very long and preponderatingly diclinous antheridial branches 

 of 6". delica are very unlike those of the Ferax group. 



Trow ('95) finds fertilization to occur in case antheridia are present. 

 He worked on material not certainly pure and called it S. ferax when 

 antheridia were absent and S. fnixta when they were in part present. 

 His conclusions covering work on both S. mixta and S. dicliua {S. dioica) 

 may be condensed as follows (in so far as we think them correct): The 

 vegetative nucleus has a distinct membrane, with chromatin material 

 and a linin network; it divides repeatedly and when sporangia are formed 

 enough nuclei enter to furnish one for each spore, no di\'ision or fusion 

 taking place in the sporangia. The oogonium receives many nuclei which 

 divide once within it and form about 20 times more than are necessary 

 to supply the eggs with one each; the excess degenerate. Most of the 

 nuclei in the antheridia and fertilizing tubes also degenerate. A single 

 male nucleus enters the egg and approaches the egg nucleus, but does 

 not fuse with it completely until a late stage. On germination the fusion 

 nucleus divides to form a number which become the nuclei of the result- 

 ing zoospores. Trow was misled, in this paper, as to the structure of 

 the nucleus, the number of chromosomes and the method of division. 

 See under S. ferax for Davis's work on a plant closely related to, if not 

 the same as, S. mixta. 



Maurizio describes in some detail a plant he took for S. mixta (1895, 

 p. II, figs. 1-3), but in it the antheridia, which were present on about 

 a third of the oogonia, were borne always (?) on stalks arising from the 



