102 



COMPARATIVE MORPHOLOGY OF FUNGI 



This developmental series finds its continuation in Blakeslea irispora 

 (Thaxter, 1914a). This species, also as Choanephora, forms under certain 

 conditions of growth, e.g., in saturated atmosphere, typical multispored 

 Mucor sporangia with large pyriform columellas (Fig. 61, 1). These 

 sporangia show a marked tendency toward degeneration: with slight 

 alteration of cultural conditions, they decrease in cross section and spore 

 number, the columella becomes smaller and disappears (Fig. 61, 2) and 

 there result forms, which only distantly resemble the original sporangium. 



Fig. 61. — Blakeslea trispora. Modifications of sporangia. 1. Original form. 2. 

 Reduced form without columella. 3, 4. Formation of exogenous sporangioles. 5. Spor- 

 angiospore from sporangiole. 6. Mature sporangiole with broken sterigma. (1 to 4, 

 6 X 260; 5 X 720; after Thaxter, 1914.) 



Under normal conditions of growth, the spore protoplasm migrates from 

 the sporangium into saccate protrusions, sessile on spherical sterigmata 

 (Fig. 61, 3) and there, by meridianal splitting, divide into three spores 

 each (Fig. 61, 4) which, as in Choanephora, bear little tufts of hairs at 

 their tips (Fig. 61, 5). At maturity, the protuberance is separated from 

 its sterigma or with its sterigma from the sporangium and is disseminated 

 (Fig. 61, 6). In this species, spore formation (in contrast to Cunning- 

 hamella) is again retarded; between the differentiation of sporangial con- 

 tent into a sterile and a fertile zone and the individualization of the 



