118 THE LOWER FUNGI— PHYCOMYCETES 



entiated. Nevertheless, the resting spore at maturity Ues free 

 in the female cell and resembles the oospore of the Saprolegniales. 

 The sexual process has been studied cytologically in only two 

 species, Myzocytium vermicolum Zopf and Ancylistes closterii 

 Pfitzer. The nuclear history in these forms is described by 

 Dangeard, and his results are discussed under these genera below. 

 Other cytological investigations are urgently needed, since at 

 present, the fundamental nature of the sexual process in the 

 various members of the group is in doubt. Not infrequently 

 resting spores are formed apparently parthenogenetically from 

 the contents of a single cell. The resting spore in all cases is 

 spherical and thick-walled. In some species it germinates by 

 swarmspores, in others by a germ tube. 



In several respects the members of the order seem to be more 

 highly developed than the Chytridiales. The resting spore lies 

 free in the female gametangium, a conjugation tube, rare in the 

 chytrids, is commonly formed, and in Ancylistes both the spor- 

 angium and resting spore germinate by germ tube. The cells 

 composing the thallus show, moreover, a greater abiUty to 

 function in diverse capacities, division of labor comparable to 

 that in higher groups being evident. In these various respects 

 the group appears to approach the Saprolegniales and is perhaps 

 to be regarded as intermediate in type between that order and 

 the Chytridiales. The group is regarded as more primitive than 

 the Saprolegniales in that mycehum is absent or poorly developed, 

 a well defined oosphere absent, and the gametangia not clearly 

 differentiated as oogonium and antheridium. In Ancylistes, 

 particularly, zygomycetous features are evident. 



The order, as here treated, contains the single family Ancy- 

 listaceae. 



Key to Genera of Ancylistales 



I. Asexual reproduction accomplished by swarmspores freed from 

 sporangia. 

 A. Mature thallus an unbranched tube, divided by transverse septa 



into a row of cells of similar size and form, usually constricted at 



the septa. 



1. Swarmspores escaping from the sporangium fully formed, 



and encysting individually at its mouth as in Achlya. 



1. Achlyogeton, p. 119 



2. Swarmspores not encysting at the mouth of the sporangium ; 



contents of sporangium usually extruded into a vesicle. 



2. Myzocytium, p. 120 



