° 
1900 | THE HAUSTORIA OF THE ERYSIPHEZ 163 
distinctly visible and its slenderness appreciable ; whereas, if it 
were not for this circumstance, the size of the tube would fre- 
quently be exaggerated. 
Nordhausen, in experimenting with Botrytis, Penicillium, and 
Mucor (23, p. 38), observed a marked browning of the epider- 
mal cells in contact with the germinating spores, which always 
preceded penetration. He thinks (p. 7) that the phenomena of | 
browning and subsequent death of the cells are due to the pro- 
duction of some poison during the germination of the spores. 
Von Mohl (34, p. 592), De Bary, Frank (14, p. 556), and others 
mention this browning in the Erysiphee. In the stained sec- 
tions this brown color is not distinguishable, though the cell 
wall around the point of penetration is more or less altered and 
dissolved. Seen from the outer surface of Poa (Zrysiphe com- 
munis) and Eupatorium (Zrysiphe Cichoracearum), there is an 
area surrounding the point of penetration which is entirely col- 
orless, clear, and shining. The remaining portions of the epider- 
mal wall stain with safranin. The outer surface of the colorless 
area is usually depressed also, the depression being deepest at 
the point of penetration, as though a part of the cellulose had 
been dissolved away. This dissolution of the cellulose suggests 
that the Erysiphee probably produce an enzyme suited to this 
work. é 
In the sections of Geranium leaves the safranin stain 
frequently makes evident the beginning of penetration, The 
first intimation of the process is a deep staining of the inner sur- 
face of the outer wall of the cell immediately under the point 
where the hypha comes in contact with the epidermis (fig. 7 ). 
This staining, however, is to be seen occasionally at the cross- 
walls of the epidermis, where haustoria have never been pro- 
duced, It is possible that it is this deeply staining spot which 
Shows the brown color in fresh material. 
The next step to be observed in the development of the 
haustoria (fig. 2) is the thickening of the epidermal wall toward 
the interior over an area coinciding roughly with the clear space 
already mentioned (fig. 17). Nordhausen (23, p- 17.) observed 
