iQ2o] THAXTER— FUNGUS-PARASITES 5 



mature condition, has not been obtained. From such young 

 specimens as have been examined, however, it is evident that a 

 proliferation takes place over the surface of the primary stage, 

 which results in the development of the structures distinguishing 

 the genus. The primary thallus thus forms a thin substratum, 

 more or less firmly coherent to the surface of the host, on which 

 the secondary stage is seated, and which is clearly distinguishable 

 both in crushed specimens and in sections; the brown chlamydo- 

 spore-like cells persisting in situ, singly or in groups. 



A section of the mature fungus, which under a hand lens has 

 the appearance of a black Hysterium when growing on the legs 

 (fig. 7), or of a small discomycete with pal^ hymenium and black 

 margin on other portions of the host (figs. 8, 9), shows a differ- 

 entiation into several distinct regions. The first is a thin dark 

 layer of cells, in which many or few of the chlamydospore-like 

 bodies may be visible at intervals, and which, in a favorable section, 

 may include the primary attachment of the fungus, an indentation, 

 associated with a group of dark cells (fig. 14) opposite which the 

 hypertrophied cells of the host are usually somewhat brownish. 

 No indication has been seen of any actual penetration of the 

 parasite through the integument of the host; but these primary 

 attachments are readily distinguished, and usually appear as a 

 limited dark area which shows through the sporogenous region 

 when the fungus is viewed vertically, as in fig. 9. 



Above this primary layer, and derived from it by vertical 

 proliferation, is a region of irregularly polygonal, hyaline cells, 

 the origin of which, as components of a series of branching hyphae. 

 is obscured or quite obliterated through unequal growth and mutual 

 pressure, and is only indicated by a tendency of the lower cells 

 to retain an arrangement in vertical rows. The thickness of this 

 region is somewhat variable, the cells becoming smaller and numer- 

 ous above; the uppermost giving rise to the straight, erect, tubular, 

 and apparently always simple filaments which compose the sporo- 

 genous layer or region. In this layer, which is four or five times as 

 thick as that from which it is derived, two regions are again 

 recognizable, the limits of which may be very clearly indicated. 

 In the lower of these regions the continuous protoplasmic content 



