DICTYUCHUS 155 



in Michigan a plant whidi, Iroin liis unpublished (k-scription and drawings, 

 we take to he this species (reported as D. monosporus in Ann. Rt]!. Mich. 

 Acad. Sci. 17: 195. i()i5). ^^'ith his consent, wc are using Dr. Pieters's 

 pencil drawings in plate 53. 



The following is from Humphrey: 



"Hyphae rather large. Zoosporangia cylindric or fusiform. Oo- 

 gonia terminal on slender branches, globular, smooth-walled, unpitted. 

 Antheridia cvlindric or slightly clavate, on all oogonia, borne on slender 

 branches of 'diclinous origin. Oospores single, centric, al)Out 25;j. m 

 diameter. 



" Massachusetts— Cambridge, Trelease. Europe. 



"Our knowledge of the occurrence of this species in America rests 

 on the notes and preparations of Professor Trelease, who obtained it in 

 1881 from water in the Botanic Garden, at Cambridge. It can be con- 

 founded onl>- with D. monosporus, from which it differs in its somewhat 

 larger oogonia and less coiled antheridial branches. 



"Lindstedt states that it is only in this species that the sporangia 

 arc formed from the hyphae in basipetal succession, but it seems doubt- 

 ful if this is strictly true, in view of certain observations to be men- 

 tioned later." We may add to these remarks that Lindstedt also notes 

 that the eggs after a rest sprout by a vegetative thread (I. c, p. 18). 



Pieters sajs: 



"Collected on a fly, from water with algae, in the Botanical Labora- 

 tory at Ann Arbor, November, 191 3. Oogonia de\-eloped on fly at tem- 

 perature 22-30^ C. Antheridia always strongly diclinous, and clasp 

 the oogonia with one or more processes. Oogonia walls thin, not pitted; 

 eggs single, centric with two to many oil drops. Sporangia will develop 

 in pea agar." He labels his notes D. monosporus, and says further: "I 

 will admit that there may be a doubt as to whether this species is mono- 

 sporus or Magnusii. I determined it as monosporus on the strength 

 of the fact that antheridia coiled around the oogonia. The size of the 

 oogonia, however, appears to be that of Magnusii rather than that of 

 monosporus." 



It is indeed extremely doubtful if D. Magnusii is a good species. 

 As described by Lindstedt it differs from D. monosporus only in three 

 characters, none of which is of any value unless established as con- 

 stant by a series of careful cultures — a precaution that one feels pretty 

 sure Lindstedt did not take. These three points of difference arc that 

 in D. monosporus the oogonia are 2^x thick, the antheridial branches wind 

 about the oogonia, and the sporangia are in sympodia; while in D. Magnusii 

 the oogonia are 30-35;;. thick, the antheridial branches do not wind about 

 the oogonia, and the sporangia are iiorne only in rows. As our sterile 



