HYPOCRELLA AND ASCHERSONIA. 177 



outgrowth from the basal portion of the stroma, but a series 

 of developing specimens seems to indicate that it is part of 

 the initial development of the fungus, the central portion 

 becoming thicker later. This structure has received the 

 name of " hypothallus." It does not underlie the whole 

 stroma, but forms merely a border at its lowest edge ; an 

 apparent exception to this rule has been found in Hypocrella 

 hispora, in some examples of which a thin, white, tomentose 

 layer underlies the stroma and projects beyond it, but it 

 appears doubtful whether this is really a part of the Hi/pocrellci 

 stroma. 



Unfortunately the hyiJothallus is not a constant feature of 

 any species, and camiot be employed to separate them. It 

 is usually present in Aschersonia placenta, but it may be 

 present or not in specimens on the same leaf. In general 

 the presence of a hypothallus is usual in the species parasitic 

 on Aleyrodidsc, but rare in those parasitic on Lecaniidss. 



Among the characters of the genus Aschersonia, Montague 

 included the presence, in the early stages, of a universal veil 

 or covering which disappeared with age, and in this he has 

 been followed by quite recent writers. But no such structure 

 exists. One is inclined to suppose that Montague assumed 

 this character from the presence of a hypothallus, but no 

 hypothallus is present, as far as I was able to discover, on the 

 type specimens of either of his species. Nor are the specimens 

 mouldy, as is the case with the type of Hypocrella epiphylla, 

 in which the surrounding circular patch of mould has been 

 described as a hypothallus. 



The term " hypothallus " appears to have been employed 

 in a very loose manner by the describers of species of Ascher- 

 sonia and Hypocrella. It should denote a thin film or layer 

 of hyphee surrounding the base of the stroma, which appears 

 quite distinct in character from the tissue of the stroma. 

 On the other hand, many scutate or flattened stromata thin 

 out regularly towards the margin, but the tissue of the stroma 

 is evidently of the same character right up to the edge. In 

 these latter cases, it is not correct to designate the thin 

 edge a hypothallus. 



