CHYTRIDIALES 63 



whether an undischarged sporangium will turn out to be operculate 

 or inoperculate, the witnessing of the escape of the zoospores is ab- 

 solutely essential to proper identification. 



In recent years the term "endooperculum" has been applied by a 

 few workers to a structure whose origin differs from that of a true oper- 

 culum. As indicated previously (p. 58), in some chytrids, notably those 

 with a prominent discharge papilla, a membrane may form over the 

 face of the protoplasm in the base of the tube. In sporangia quiescent 

 for a period after maturity this membrane may thicken and become 

 rigid and even umbonate. Such structures have been observed in a 

 number of chytrids belonging to different genera, both inoperculate 

 and operculate. It is not, however, produced by all sporangia in all 

 cultures. Certain species and strains seem more prone to form it than 

 others. That it does form sometimes has been attested to by competent 

 observers of these fungi. 



Considerable taxonomic stress has been laid on this secondarily 

 developed protective coating for the contents in more or less quiescent 

 sporangia by Johanson (1944). As a result, she segregated species of 

 Rhizophlyctis that form it into a distinct genus, which she named 

 Karlingia (see Karlingiomyces, p. 559). Haskins (1948), however, sub- 

 sequently made an extensive study of many strains of the species that 

 Johanson designated the type of "Karlingia" the ubiquitous R. rosea 

 de Bary and Woronin. He discovered that in some of these strains 

 zoospore discharge often took place before there was any evidence 

 of an endooperculum. His observations confirm our own studies on 

 this species with respect to variability in endooperculum formation. 

 Note, too, that in discussing another chytrid, Diplophlyctis sexualis 

 Haskins {op. cit.) comments: 



Our species in rapidly growing cultures, dehisces in a normal inoperculate 

 manner and occasionally after extrusion of a gelatinous plug, but in older 

 stagnating cultures, after the deliquescence of the gelatinous tip of the exit- 

 tube has occurred, the membrane between the protoplasmic contents of the 

 sporangium and the external medium thickens. This membrane may thicken 

 so as to form an endo-operculum-like structure, which at subsequent dehis- 

 cence of the sporangium may merely rupture or may be forced out as a cap 

 as described for Nephrochytrium amazonensis (Karling, 1944 [e]). 



