176 FETCH : 



are actually parasitic on the latter, but must depend for their 

 supply on the rain or dew which falls on the leaf. They must, 

 therefore, be adapted to withstand periods of drought. 



In general the stroma is solid, though in some of the Aley- 

 rodiicolse the hyphse are somewhat loosely interwoven, and a 

 section shows numerous interspaces. Species which have been 

 described as " eroso-excavatis " prove, on examination, to 

 have been hollowed out by insects (? beetles). In most of the 

 available specimens of Aschersonia Tamurai, however, a small 

 hollow space occurs in the centre of the base, without any 

 evident sign of insect injury. 



As a rule, the stromata of the Lecaniicolous species are 

 harder than those which are parasitic on Aleyrodidse. This is 

 due to the more compact arrangement of the hyphse, and, 

 in part, to a greater thickening of the walls of the hyphse in 

 the former. This feature, however, cannot be employed as 

 a generic character, as in the genus Fleischeria proposed by 

 Penzig and Saccardo, since, apart from the difficulty of 

 establishing standards of hardness, it would necessitate the 

 separation in different genera of species which are undoubtedly 

 co-generic. All grades of hardness exist, among the Lecanii- 

 colous species, from Hypocrella Schizostachyi, the hardest 

 species known, to Hyjiocrella convexa, which is no harder than 

 many of the Aleyrodiicolse, and it is not possible to define the 

 degree of hardness which would qualify a species for inclusion 

 in the genus Fleischeria. 



In some cases the lumina of the hyphse are filled with 

 yellow globules, e.g., in some collections of Hypocrella Eeinec- 

 kiana. This, again, is not a constant feature of any species, 

 and there are indications that it varies according to the age 

 of the stroma. The stroma is not gelatinous, i.e., it does not 

 absorb moisture and swell up when wetted. The contents of 

 the hj'phse stain with cotton blue, but the walls do not . 



In many species an extremely thin la^^er of hyphse borders 

 the base of the stroma, sometimes extending from it for one 

 or two miUimetres, closely applied to the surface of the leaf. 

 It may be tomentose, its hyphal structure being clearly 

 evident under a slight magnification, or the hyphse may be 

 fused into a membranous transparent film. It appears an 



