82 THE SAPROLEGNIACEAE 



The genus is characterized and distinguished, in the main, by the 

 presence of the cymose or Achlya mode of formation of secondary spor- 

 angia, coupled with diplanetic zoospores. 



The al)ove is copied without change from the original description 

 except for the addition of the words "or eccentric" in speaking of the 

 oospores, so as to admit our new species, /. eccentrica. It should also 

 be added that the genus is characterized by the great scarcity of an- 

 theridia, which are absent in three of the species and few in the other one. 

 In his new genus KaufTman proposed to include /. toniloides, our Achlya 

 paradoxa and Saprolegnia monilifera. After looking over the matter 

 carefully we have concluded that while /. toniloides and 5. monilijem 

 should be put here, together with our two new species, I. unispora and 

 I. eccentrica, it would not be well to add to them A. paradoxa, which 

 differs materially. For the latter we propose the genus Protoachlya. It 

 is quite possible that other species of Saprolegnia, such as S. curvata, 

 S. torulosa, S. rhaetica, S. variabilis and S. bodanica, might be referred 

 to Isoachlya if better known. 



Key to the Species 



Antheridia present on some (less than half) of the oogonia /. toniloides (l) 



Antheridia absent 



Eggs usually 1-2 in an oogonium, centric !• unispora (2) 



Eggs usually 1—2 in an oogonium, eccentric I- eccentrica (3) 



Eggs usually 2-6, centric /• monilifera (4) 



I. Isoachlya toruloides Kauffman and Coker. Am. Journ. Bot. 8: 

 231, pis. 13 and 14. 1921. 



Plate 21 



Threads delicate but vigorous, moderately branched, thickened 

 towards the sporangia, reaching a length of about 6-8 mm. on a mush- 

 room grub. Sporangia nearly cylindric to clavate or irregular, pro- 

 liferating from within, or less often laterally as in Achlya, usually broad- 

 est near the papillate tip, moderately abundant throughout the growth 

 of the culture. Spores diplanetic, 1 1.5-12.511. in diameter during the first 

 resting stage, at times sprouting through the wall of the sporangium 

 as in Aplanes (net-sporangia not seen). Oogonia abundant, mostly 

 spherical, not rarely oval or pyriform even though apical, at times pointed 

 or otherwise irregular and rarely cylindrical in empty sporangia; with 

 or without a neck; in young cultures mostly borne singly at the tip 5 of 

 main hyphae, later appearing throughout the culture on bent or crooked 

 lateral branches about 1-3 times the length of their diameter, these stalks 

 often sending out near the oogonium a lateral branch which bears an- 

 other oogonium on its tip; in older cultures often intercalary (single) or 

 two or three in a row (moniliform) ; at times a good many may be borne 

 singly just outside the mouth of empty sporangia by the through growth 

 of the threads that bear them; walls thin, about i.3ij. thick, colorless, 



