DICTVUCHUS 151 



rather hliint. Primary sporangia nearly cylindrical, blunt, borne typi- 

 cally in a zigzag sympodiuni with long internodcs; later they arc formed 

 by the segmentation of the hyphae into long joints and in such case, 

 after the spores are formed, rest like gemmae for a change of media 

 before liberating the spores, and show a strong tendency to fall away 

 from each other and from the hyiihae and to lie free in the water. Spores 

 not escaping from the sporangium as in other genera (except Aplanes), 

 but remaining in the sporangium and forming there a network of walls 

 from which they emerge, after a rest, by individual openings to the out- 

 side, where they swim by two cilia and in the form of the second swimming 

 stage in Saproleguia. They then, as a rule, sprout as usual in the family 

 but Weston ('19) has show^n that some of them may again emerge and 

 swim before sprouting. Gemmae not represented unless the resting 

 sporangia with spores in them be considered such. Oogonia spherical, 

 smooth, the wall unpitted, terminal on slender branches (absent (?) in 

 D. sterile). Antheridia much as in Saproleguia and Achlya, diclinous 

 or androgynous; fertilizing tubes observed. Eggs one to many, not 

 filling the oogonium, at maturity containing one or a few large oil drops 

 inside the protoplasm. 



Key to the Species.* 



Oogonia unknown (plant never fruiting) ; sporangia apt to drop off in a resting state 



D. sterile (i) 

 Oogonia with one egg 



.Antheridia and antheridial branches not surrounding the oogonia D. Magnusii (2) 



.■\ntheridia with the antheridial branches often thickly encircling the oogonia 

 Hyphae here and there branched in a normal way; eggs centric 



D. monosporus (p. 156) 

 Hyphae with irregularK arranged, mostly short, papillose outgrowths with an abnormal 



appearance; eggs eccentric D. carpophonis (p. 157) 



Oogonia with many eggs D. polysporus (p. 1 57) 



I. Dictyuchus sterile n. sp. 



Plate 52 



\'egetative growth moderately stout. Main h\-phae branching, up 

 to 551JI. thick, mostly 30-45^1 at base, very gradually tapering towards 

 end, the larger up to 22-37^1 near tip, many much smaller. Primary 

 sporangia borne on the tips of hyphae, later ones formed by cymose 

 branching, but usually separated from the earlier ones by some distance 

 by the elongation of the threads. As the culture ages the arrangement 

 becomes more irregular and complicated and most of the threads become 

 segmented towards the peri[;hery into numerous sporangia in rows or 



*Taken from Minden, except for the addition of the Chapel Hill plant. The American 

 species are followed by a number, the others by a page reference. 



