84 THE SAPROLEGNIACE^ OF THE UNITED STATES, 



tion of the hyphse, the absence of sexual organs in most species, and their peculiar- 

 ities in the single species in which they are known, with minor variations, of little 

 weight individually, which distinguish the species of Leptomitus and A.-podaclilya 

 from the others of the family, justify their separation as a distinct subfamily. The 

 discovery of sexual organs in one of these plants, on the other hand, confirms the 

 indication of the zoospores that they should be included in the present family. Set- 

 ting them aside, then, as Leptomiteoe, we may examine the genera constituting the 

 SaprolegniecE, 



It is evident that the most primitive condition as regards the zoospores is pre- 

 sented by the typically diplanetic form, as found in 8aprolegnia. But the renewal 

 of sporangia occurs most commonly, and apparently most typically, by latei"al, 

 cymose branching. Assuming as the primitive form an hypothetical one combining 

 the two characters above indicated, we must place first in the series Saprolegma and 

 Lfptolegnia, difiering from it only in respect to the second point. Pythiopsis has 

 economized by suppressing the second swarming stage, and stands alone on this line 

 of development. In Aclilya the first swarming has been reduced to a minimum by 

 the mutual attraction of the spores, a newly acquired feature, and Aphanomyces 

 seems best regarded as a degenerate Achlya rather than as a primitive one. In the 

 remaining genera the reduction of the first swarming stage, begun in Aclilya, is 

 carried to complete suppression. The condition presented by a dictyosporangium of 

 Aclilya is in the direct line of development from the normal type of that genus, and 

 that of the aplanosporangium is a further step on the same line. The former condi- 

 tion becomes modified in two ways — in Tkraustotheca, by the early breaking up of 

 the sporangial wall; and in Dlctyuchus, by the coalescence of the encysting walls 

 and the development of numerous secondary mouths instead of the original primary 

 one. The latter condition becomes permanent and typical in Aplanes. 



