a 
NOTES ON THE ERYSIPHACEAE 205 
(¢f. figs. on pl. ro, rr). Considering the peculiar shape of the 
penicillate cells shown by some forms we may perhaps suspect that 
in such variation there is to be found the origin of an incipient 
species—in other words that throughout the geographical range of 
Pf. corylea an incipient species is evolving on these lines from the 
parent form. The characters of this form, however, are not yet 
sufficiently sharply marked off, and are altogether too sporadic in 
appearance to allow us to give the form a place in systematic clas- 
sification, . 
As is now well known, the apex of the perithecium of P. 
corylea is provided with a mass of penicillate cells—outgrowths 
from the external cells of the perithecial wall—which at a certain 
stage in the ripening of the perithecium and probably under cer- 
tain external conditions, become mucilaginous and perform a 
curious function in the life history of the species. At the stage 
referred to the perithecium bears a large whitish mucilaginous 
drop on its upper surface. Neger (54) mentions that he has 
observed swimming about in isolated patches over the suiface of 
this drop a foam-like mass, the separate bubbles of which bear a 
Strong resemblance to polygonal thin-walled cells. This is evi- 
dently, as Neger observes, the structure represented by Tulasne 
(Carpologia, 1 : pl. rz. f. 2, 5, 6) asa continuous cellular membrane 
covering over the penicillate cells. In contact with water the 
cellular appearance of this mass is soon lost, and the whole dis- 
appears, leaving nothing behind but a mere trace of a hyaline 
mucilaginous substance. Neger states that the foam-like mass, 
together with the mucilaginous drop, is excreted from the peri- 
thecium. By a mechanism to be described later, the attachment of 
the perithecia to the leaf is destroyed, and each perithecium stands 
free on the points of its reflexed appendages among the hairs, 
etc., of the leaf, and is liable to fall at the slightest touch to the 
leaf or to be blown away by a breath of wind. At this stage the 
wall of the ultimate branches of the penicillate cells breaks 
down into a mucilaginous substance. When the fungus reaches a 
new substratum, the reflexed position of the appendages causes 
the apex of the perithecium, bearing its drop of mucilage, 
ones. or later to come into contact with the surface of the 
| FCs on which the perithecium has fallen. The mucilage 
