WITH NOTES ON OTHER SPECIES. 117 



of this family, so far as the writer's observations go, while closely resembling the two 

 commonest European species, combines their characters in a peculiar manner. Like 

 A. prolifera, our form has oogonia with abundantly and invariably pitted walls ; but, 

 like A. DeBaryana, its antheridial branches are of androgynous origin ; and, like 

 both, its oospores are of excentric structure. The pits of the oogonial walls are not 

 conspicuous as in the Saprolegmoe of the ferax group, although they are usually 

 of considerable size; but treatment with the chloroiodide of zinc always brings them 

 out, as numerous transparent areas in the elsewhere deeply colored membrane. The 

 antheridial branches are not so long nor so luxuriant as those of A. DeBaryana, as 

 figured by DeBary ('81). They usually arise quite near the oogonial branches, very 

 rarely even from the latter, which is said by DeBary never to happen in the last-named 

 species ; and the antheridia are rather shorter and envelop the oogonia less than is the 

 case with the other. 



These rather slight, but very constant, differences seemed at first to invalidate the 

 distinction between the species called by DeBary A. prolifera and A. polyandra, and 

 to indicate that they, with the present, are forms of a single variable species. But 

 the very positive statement of so reliable an observer as DeBary as to the constancy 

 of the characters of his two forms,* and the abundant evidence of repeated cultures 

 from widely separated sources of the fixity of the present one, have left no alternative 

 but to consider the three as distinct, though closely related, species, forming a series 

 whose middle member is our American representative, and which may be termed 

 the "prolifera group. 



I have met with this species in no less than twenty cultures from clean waters 

 of every description, and from various parts of the country. It is the form referred 

 to by the writer in an earlier note ('91) as "a form related closely to A. polyandra 

 (perhaps that species) ;" and is that in which I first convinced myself of the pres- 

 ence of cilia on the escaping zoospores of Aclilya. 



Aclilya DeBaryana, nom. nov. 



Syn. : A. polyandra DeBary ('81). 111. : DeBary, '81, Pi. IV, Figs. 5-12. 



Ward, '83, PI. XXII, Figs. 1-14. 



This is, as already stated, one of the commonest European species, but it has not 

 been recognized in America. It has smooth, unpitted oogonia and long, branched 



*I am indebted to Prof. Alfred Fischer, of Leipzig, who has had the opportuuity of studying DeBary's material, 

 for a full confirmation of that author's statements concerning tliese species. 



