64 AQUATIC PHYCOMYCETES 



On the basis of Haskin's observations, our own on such species as 

 Nowakowskiella macrospora Karling, and accounts of the process in 

 Karlingiomyces {Karlingid) granulatus, we conclude that endoopercu- 

 lation can occur in any chytrid, under certain environmental conditions, 

 particularly with age. Moreover, Hanson (1945a: 438), in a discussion 

 of relationships of certain chytridiaceous fungi, states that she considers 

 the endooperculum a "generically invalid" character. 



With respect to Karlingiomyces {Karlingid) granulatus and Nowa- 

 kowskiella macrospora, described as having both a true operculum and 

 an endooperculum, Haskins (1948) says that these "require further 

 study to determine the composition of the exo-operculum [true oper- 

 culum] as it exists in these forms. If it is of the same substance as the 

 inner wall, then the condition is at one of the extremes of endo-oper- 

 culation. If it is truly an exo-operculum in composition and origin, 

 as well as appearance and function, then it is a form for which allow- 

 ances must be made in any scheme of classification. " In the few cases 

 in which Haskins observed exooperculation and endooperculation in 

 the same plant, he believes that the apparent exooperculum was not, 

 in fact, derived from the original sporangium wall and, hence, was 

 not a true operculum. 



We agree with Haskins {op. cit.) when he states: 



The term [operculum] should be reserved for a very definite and discrete 

 structure, an actual portion of the original sporangial wall, which, because 

 of a thinning and weakening of a circumscissile linear region of that wall, 



lifts off" or hinges as a cap or lid upon dehiscence of the sporangium The 



condition where the sporangium is actually inoperculate, but a secondary 

 structure is formed across the base of the discharge tube or in it, may be 

 conveniently termed 'endo-operculate,' remembering its closer association 

 with the inoperculate rather than the operculate condition. 



Internal proliferation of the sporangium by a renewal of growth 

 and expansion of the nucleated apex of the rhizoidal stalk which grows 

 up through the base of the previously formed, now empty, sporangium 

 has been observed in both monocentric (for example, Loborhiza and 

 Phlyctochytrium proliferum) (Fig. 19, J, p. 318) and, more commonly, 

 in polycentric chytrids {Cladochytrium, Nowakowskiella [Fig. 35 

 H-I, p. 583], Polychytrium, and Physocladid). It also occurs in the 



