HYPOCRELLA AND ASCHERSONIA. 183 



suggests that the pycnidia were originally merely depressions 

 in the surface of the stroma ; indeed, many of the shorter 

 tubular pycnidia give the impression that they are formed by 

 the development of the basidia on a small area, and the 

 subsequent lag of the growth of that area behind that of the 

 surrounding tissue of the stroma ; and the mere flask-shaped 

 or elongated-oval pycnidia could be derived from the tubular 

 form by the constriction of the orifice. But in other cases, 

 e.g., in Hypocrella olivacea, the oval pycnidium is formed 

 within the tissue of the stroma. The small forms of Ascher- 

 sonia cubensis show very interesting variations in this respect ; 

 in fully-developed forms the apex of the stroma is umbilicate, 

 and the globose pycnidium, which hes within the body of the 

 stroma, opens at its highest point into the funnel-shaped 

 depression. In some immature examples, however, there is 

 no pycnidium in the body of the stroma, but a superficial 

 layer, apparently of developing basidia, at the base of the 

 depression. 



In the Aleyrodiicolse the pycnidia may be elongated-oval 

 or almost flask-shaped, as in Hypocrella Mollii ; or definitely 

 globose or flattened-globose, with a distinct conical neck, as 

 in the discoid species, Hypocrella discoidea, Aschersonia flavo- 

 citrina, &c. ; or widely and irregularly open, as in Aschersonia 

 placenta, A. Aleyrodis, A. hypocreoidea, &c. The first two 

 types are formed within the tissue of the stroma ; and the 

 pycnidium of the discoid species opens by a distinct pore 

 in the centre of a thin scarious area. But the pycnidium 

 of the third type may originate either superficially or 

 internally. 



This latter type of pycnidium is an irregular cavity, circular 

 or oval in plan, usually with a convoluted base. In the case 

 of very thin stromata, such as generally occur in Aschersonia 

 hypocreoidea, it is undoubtedly^ formed superficially, i.e., by 

 the development of basidia on the surface of the stroma. 

 In other species, e.g., Aschersonia placenta and Aschersonia 

 Aleyrodis, the stromata may vary from mere films to a thick- 

 ness of 1 -5 millimetres, and though the basidia are produced 

 superficially in the former, it is doubtful whether the same 

 is true of the thicker stromata. Webber has described 



6(9)21 (25) 



