854 AQUATIC PHYCOMYCETES 



and seemingly have unlimited powers of continued growth and branch- 

 ing. They are conspicuously constricted at more or less regular 

 intervals (Fig. 69 E, p. 875), the constrictions being partly plugged by 

 pseudosepta consisting of a somewhat refractive material termed "cel- 

 lulin" by Pringsheim (1883a). These constrictions of the main hyphae, 

 and of the branches which may arise immediately beneath them, give a 

 characteristic jointed or segmented appearance to the whole thallus. 

 The contents, at least in Apodachlya, are rather lustrous and, in both 

 this genus and Leptomitus, possess occasional conspicuous refractive 

 discs of cellulin. These discs, according to Radais (1898), may sometimes 

 act as "corks" to plug up accidental tears in the hyphal walls. 



In the Rhipidiaceae the thallus is always somewhat arborescent and 

 more or less strongly differentiated into a basal cell, derived from the 

 body of the germinated zoospore (Minden, 1916), and into hyphal 

 branches which arise from its distal portion (Fig. 70 C, p. 890). The 

 basal cell is anchored in the substratum by a system of tubular some- 

 times locally expanded holdfasts. These evidently perform the same 

 function as the rhizoids of the Chytridia'es and Blastocladiales, that is, 

 anchorage and absorption, but they appear to lack the characteristic 

 strongly tapering "chytrid-like" aspect. In some species the basal cell 

 may be slender and scarcely differentiated from the hyphae, as in Sap- 

 romyces (Fig. 70 A). In others, such as Rhipidium, it may be very 

 trunklike, with a "monstrously developed," strongly expanded, lobed 

 and gnarled distal part which forms a platform from which the hyphae 

 and reproductive organs arise. The walls of the basal cell are frequently 

 of considerable thickness, colorless or somewhat brownish (especially 

 with age), and occasionally roughened on the outer surface (Kanouse, 

 1927). Whatever the extent of development of the basal apparatus, the 

 hyphae arising from it (except in Mindenielld) are always marked off at 

 their point of origin by a constriction containing a more or less well 

 developed pseudoseptum of cellulin. As in the Leptomitaceae, these 

 hyphae have occasional constrictions along their length (Fig. 70 A). They 

 may remain simple or be sympodially branched. 



This curious differentiation of the thallus into rootlike holdfasts, 

 trunklike basal cell, and branches is clearly evident in Rhipidium and 

 Araiospora, and to a lesser degree in Sapromyces. Although branches 



