HYPOCRELLA AND ASCHERSONIA. 175 



of 14 (X in Fleischeria sclerotioides {Ilypocrella olivacea). The 

 lumen is reduced to one-third or one-quarter of the diameter 

 of the hypha, and the septa are inconspicuous. The thickened 

 walls frequently exhibit lamination. Towards the periphery 

 of the stroma the ends of the hyphse may, especially in the 

 Lecaniicolous species, form a distinct epidermal layer, either 

 pseudoparenchymatous, or of short parallel " cells." In some, 

 more especially the Aleyrodiicolous species, the ends of the 

 hyphse form a minutely tomentoso layer. In the centre of the 

 stroma, at the base, in the position originally occupied by the 

 host insect, the hyphse, probably those which at first permeated 

 the body of the host, are usually thinner ; in many examples 

 of Lecaniicolous species, this region is defined by a red sub- 

 hemispherical zone, or is sometimes entirely red. 



As far as has been observed, the hyjjhse of the stroma do not 

 penetrate into the leaf on which it occurs. A slight pressure 

 is sufficient to detach the stroma from the plant, a fact which 

 accounts for the loss of specimens of the fungus in many 

 herbarium examples. When detached, it is seen that the 

 base of the stroma in many Lecaniicolous species is not 

 uniform ; the outer portion is usually smooth and glabrous, 

 indicating that in that region the constituent hyphse were 

 merely adpressed to the surface of the leaf ; the central portion 

 which marks the position of the host insect is often powdery 

 or rough, and bordered by the red zone previously referred to. 

 This is not a constant feature, but some modification of it can 

 usually be traced. Owing to the looser texture of the central 

 area, a small part may remain adherent to the leaf when the 

 stroma is detached. Thus, both on the stroma and the plant, 

 traces of the previous attachment may persist, and these 

 constitute what I have previously referred to as the character- 

 istic Hypocrella " scar." 



It will be recognized that the structure of the stroma 

 resembles that of a sclerotium. The hj'phse are irregularly 

 intertwined, have thickened walls, and are fused together 

 into a compact mass. This is, perhaps, to be correlated with 

 the habit of these fungi. They are parasitic on scale insects, 

 not on the plant on which they occur. They are not able, 

 therefore, to obtain water from the plant, as are fungi which 



6(9)21 (24) 



