ACHLVA 97 



seen that show the conspicuous winding of the anthcridial Iiranches 

 about the hyphae.* Aclilya iiuperfecla is just Hkc ,1. proliferoides ex- 

 cept that it has as many androgynous as diclinous anthcridia and that 

 the antheridial branches do not wind about the hyphae. These two 

 also show the odd peculiarity' (sharetl to a less extent by ^I. JIaaellata) 

 of failing to de\-elop the great majority of their eggs to maturity. It 

 would seem that such a character could not fail to attract remark if 

 observed in related European plants, f but of this we cannot be sure. 

 This peculiarity and the great variability of this group suggest the possi- 

 bility of a hybrid origin. See Science, April 4, 1914, The Mutation Myth. 

 The main difficulty that led Humphrey to set up his A. americana 

 was the supposed absence of pits in the European plant, as stated by 

 all authors until recently. In 19 10 Petersen ('10, p. 524) reported a plant 

 from Denmark like A. polyandra deBary except that the oogonium wall 

 was pitted, and lists it as A. polyandra forma Americana, supposing it to 

 be Humphrey's plant and reducing it to a variety (egg measurements 

 not given). He did not tind a similar plant without pits. As the pits are 

 very inconspicuous and are absent on many of the oogonia it is easy to see 

 how deBary might ha^"e o\'erlooked the pits if they were absent on cer- 

 tain oogonia especially examined for this point. The pits are as whim- 

 sical as in .4. flagellata and are sometimes absent over a large part of a 

 culture and present in another part. Most authors since deBary, in 

 following his authority, might easily have been misled. The pits are 

 as a rule practically in\'isible under low power and are not so obvious 

 under any power as in many Saprolegnias. Horn found ('04, p. 227) 

 that while his plant was without pits in normal media, obvious pits 

 appeared when cultivated in peptone and in grape or cane sugar. In 

 such cases pitted and unpitted oogonia appeared on the same hyphae, 

 as is normally the case in our A. imperfecta, A. flagellata, and A. con- 

 spicua. 



The following brief diagnosis of known forms of the Prolifera group 

 showing the principal differences may be of interest: 



Achlya americana: Wall pitied; antheridial bramhes practically all androgynous, branched, 



but short; eggs small, of moderate number. 

 Achlya americana var. cambrica: Wall cunsijicuou^K pitted; antheridial branches all (?) 



andrf)gynous, on all oogonia, short and rallicr simple; eggs of medium size (2,^-26^) 



and moderate number (usually 3-S). 



* Coiling may occur to a slight extent in almost any species, as in P. paradoxa (pi. 26, 

 fig. 11). See also similar coiling in /I. polyandra as shown by Cornu ('72, pi. l). 



fHorn shows proliferating oogonia and abnormal empty ones in a plant he toolc to be 

 a form of .1. deBaryana ('04, fig. 19). 



