APHANOMVCES l6l 



Oogonial walls uneven or tuberculate, not spiny.eggs ifi-iS-^A* thick .1. scaber (2) 



Oogonial walls with distinct spines or papillae 



Oogonia 22-3> thick (including pai)illae) \ ^- ^'^""'"^ (3) 



I A . coniger (p. 168) 



Oogonia 14-22^ thick -l- parasiticfl^(,4) 



Oogonia 40-50^ thick, the wall hyaline .1- phycophilus (3) 



As above, but oogonial wall brciwii .1. non'cg,iciis (]). 168) 



I. Aphanomyces laevis dcBary. Jahrl>. f. wiss. Bot. 2: 179, pi. 20, 



figs. 17-18. i860. 



Plates 30 and 33 



Hyphae saprophytic or rarely parasitic on desmids and diatoms (see 

 below)", slender, much branched, about 5-7.5tJ- thick. Sporangia long and 

 of the same size as the hyphae, often extending to the substratum. Spores 

 7.3-1 i^j. in diameter after emerging, most about Q-iOji, rod-shaped in 

 the sporangium. Oogonia terminal on short lateral branches, glob- 

 ular or nearly so, with smooth thin walls without pits, 18-33^1 in diam- 

 eter. Eggs single, 16.5-2611 in diameter, mostly about 19-22:;., thick- 

 wallcd, eccentric, with one very large fat drop enclosed in the proto- 

 plasm and very near the surface on one side. Antheridial branches very 

 abundant, sometimes twining around the oogonial branches in a knot, 

 androgynous or diclinous. Antheridia large, abundant on all oogonia 

 and extensively wrapping them about; antheridial tubes developed and 

 plainly visible. 



This species has been recognized three times in Chapel Hill col- 

 lections; from Lone Pine spring (September), and from New Hope Creek. 

 It has probably been collected at other times, but not recognized on 

 account of its failure to fruit. It was found by Humphrey at Amherst, 

 Massachusetts, by Pieters at Ann Arbor, Michigan (Ann. Rep. Mich. 

 Acad. Sci. 8: 27. 1905), and we have obtained it mixed with A. americana 

 from a vial of water with a little trash sent us in June, 1920, from Woods 

 Hole, Massachusetts, by Mr. George M. Gray, Curator of the Marine 

 Biological Laboratory. It is easily distinguished by its smooth oogonia 

 from all except the smoothest forms of A. scaber, and from it by larger 

 eggs, and large and numerous antheridia. For other illustrations see 

 Humphrey ('92), pi. 20, figs. 105-107; and Petersen ('10), fig. 3c. 



In a collection of algae and trash from a branch near Wilmington, 

 N. C, Dec. 30, 1921, there appeared diatoms and chains of desmids on 

 which grew parasitically a species of Aphanomyces which pro\-ed to be 

 A. laevis fpl. 50, fig. 17). The threads, which were 3-6.6;x thick, en- 

 tered the living cells of the algae where they formed a branched and 

 more or less contorted and undulated complex which finally destroyed 

 the contents of its host. All reproductive parts were borne outside 

 the algae. Sporangia typical for the genus; spores 8.5-iO;j. thick. Oogonia 

 22-32^ thick; walls sinuous but without warts or spines. Eggs single, 



