142 THE SAPROLEGNIACEAE 



Fischer uses the form A. polyandra (Hildb.) deB., and treats it 

 in the sense of deBary, remarking that Hildebrand's original form is 

 an approach to A. gracilipes deB. and stands between it and A. poly- 

 andra deB. From Fischer's description we take the following addi- 

 tional data: 



Main threads ioo-i50tJi thick; sporangia, e.g., 45 X 280^^, often very 

 large; oogonial stalks 1-3 times as long as the diameter of the oogonia, 

 8-141J. thick; oogonia 45-65,jl thick; antheridial branches 8-14:0. thick, 

 1-4 for each oogonium; eggs 3-10 or more, rarely only i or 2, diameter 

 18-2511., certainly eccentric, germinating into mycelium or a sporangium, 

 resting period 21-37 days. Von Minden ('12) accepts Humphrey's 

 name, and seems to take his description from Fischer. He describes the 

 ^-ar. intermedia (which we find and are treating as a species). 



DeBary does not give the size of the eggs, but his figures (1. c, '81) 

 show the eggs distinctly larger than those of A . prolifera on the same 

 plate, at the same magnification. 



The species is apparently nearest A. americana. For a comparison 

 with this and others of the same group see under the genus and under 

 A. flagellata. For other illustrations see Ward ('83), pi. 22, figs. 1-14; 

 Zopf ('90), fig. 45; Minden ('12), fig. 2e on p. 520; Horn ('04), figs. 1-2 1. 



Trow has fully proved sexuality in this species ('04). The phe- 

 nomena are about the same as shown in his earlier paper on Saprolegnia 

 diclina and 5. mixta except that he claims (probably incorrectly) that 

 after the first division of nuclei in the oogonium a second occurs in at 

 least some of the daughter nuclei in which the chromosome number is 

 reduced, apparently, from eight to four. All nuclei now degenerate 

 except one for each egg. The egg nucleus shows a centrosome with 

 astral rays and so does the sperm nucleus soon after it enters the egg. 

 These bodies are not to be seen after complete fusion of the nuclei. One 

 division of at least some of the nuclei in the antheridium occurs, followed 

 by a slow degeneration of some of them. 



Mucke has since studied oogenesis in this species ('08) and fully 

 confirmed the occurrence of fertilization, but denies that there is a sec- 

 ond division in the oogonium or a reduction of chromosomes before 

 fertilization. Work by Claussen and Davis on Saprolegnia and by 

 Kasakanowsky on Aphanomyces shows only a single nuclear division 

 in the oogonium and leads us to believe that Trow was wrong in this 

 respect, though clearly vindicated in his hard-fought contention for 

 sexuality in the Saprolegniaceae. Mucke concludes that there are more 

 than eight chromosomes in the nuclei of the oogonia, the number being 

 undetermined. He also claims that the centrosome is inside the nuclear 

 membrane and not outside it, as Trow thought, and that the centrosome 



