168 BOTANICAL GAZETTE [MARCH 
stretched and turgid, and none of the solid contents of the host- 
cell approaches nearer to the haustorium than the outside of this 
sheath-membrane. That this membrane is so tensely stretched 
shows that it was filled with a liquid when the material was 
fixed. It, therefore, possessed osmotic qualities similar to the 
plasmic membrane of the host-cell. It has been mentioned that 
the plasmic membrane of the cell, by the activity of which the 
cellulose papilla was produced, extends over the papilla (jg. 4). 
In fig. 7 this plasmic membrane is stretched and enlarged 
extraordinarily until its origin would not be easily recognized. 
From what has been said on the development of the haus- 
toria, it is easy to understand the nature of the sheath around 
the haustorium, with its bounding membrane. That is, it does 
not belong to the protoplasm of the cell as De Bary supposed, 
nor is it the host-nucleus as Rosen observed in Puccinia; but the 
contents of the sheath consist of disintegrated cellulose from the 
distal end of the cellulose ingrowth through which the haus- 
torium has made its way. The bounding membrane of the 
sheath, on the other hand, is the plasmic membrane of the host- 
cell stretched and greatly enlarged by the osmotic forces 
involved. Inso far only does the sheath belong to the proto- 
plasm of the cell, and not at all in the sense which De Bary had 
in mind. There is abundant evidence from various sources to 
support the view just stated. Marshall Ward (35, p- 359) has 
shown that Botrytis produces a swelling and gelatinization of the 
cell-walls of the lily leaves. Ward found that the fungus was 
able to live on this disintegrated cellulose. It is well know® 
that certain fungi produce ferments which are able to digest 
cellulose. Ward found such a ferment in Botrytis (pp. 343-346): 
So also Beyerinck (8) found that Coryneum Beyerincku makes use 
of a dissolving ferment. Nordhausen (/. c., p. 38) has shown 
that Botrytis, Penicillium, and Mucor can enter a cell-wall and 
grow through it parallel to its surface for comparatively lon 8 
distances. Indeed, this power of disintegrating cellulose 
probably generally possessed by fungi, parasitic and saprophy ee 
The Erysiphee probably have such a ferment. The parti 
