300 THAXTER. 



detect, from their small size and much paler color. The process of 

 conjugation is not progressive in the developing mass; but occurs 

 almost simultaneously throughout it, the rather rapid enlargement of 

 the whole being due to the simultaneous increase in size of the indi- 

 vidual zygospores. The gametes are subequal, and do not differ from 

 one another more than is frequently the case in other isogamous types. 

 They are subcylindrical and lie parallel to one another, distinguished 

 by a clean cut septum at some distance below their adherent tips. 

 Figure 1. The developing zygospore rises from this point of contact, 

 above and between the extremities of the gametes, Figures 2-6. The 

 successive stages in this process are not unlike those figured by \ an 

 Tieghem (1873), PI. Ill, figs. 88-93, in Synccphalis cornu. 



Before full maturity, the hyphal elements of the mass are con- 

 spicuous, and rather characteristic from their large size, their branching 

 and the development of vesicular swellings which I have assumed to 

 be the "vesiculi multo minores" mentioned by Link, and which are 

 referred to by Bucholtz as " stellenweise verbreiterungen." As the 

 zygospores mature, these elements become compressed between them, 

 and may be hardly recognizable, their flattened remnants forming, 

 in many cases, an irregular envelope about the individual spores. 



The branching terminations of the filaments which form the super- 

 ficial tomentum are well figured by Bucholtz (1911), fig. 77, and 

 possess great individuality, Figure 7, but are not always conspicuous 

 in older individuals. The prominence of this tomentum varies greatly 

 in different individual masses, and under different conditions. It 

 seldom seems to be so copiously developed as is represented in the 

 figure of Link, which is evidently somewhat diagrammatic, and in 

 older specimens may appear to form a rather even covering of appar- 

 ently nearly uniform elements. 



The description given by Schroeter of Endogone xylogcna corre- 

 sponds so closely to this species, that I have included it as a synonym. 

 It seems quite improbable that the plant which he examined could 

 have been the Protomyccs xyhgenns of Saccardo; since the latter is 

 without hyphae, and corresponds in all respects to the sclerotium- 

 condition, "Phylloedia," of some myxomycete: its habitat, buried in 

 soft rotten wood and exposed only by the weathering of the latter; 

 its yellow color, and the general appearance of its spores, being the 

 same. The figures given by Saccardo (1877) in the Fungi Italici, 

 fig. 104, show the somewhat irregular outline and the characteris- 

 tically thickened, but ill defined, walls of this well-known condition of 

 the myxomycete plasmodium. 



