ba Vee 
1900] THE HAUSTORIA OF THE ERYSIPHE 175 
distance from the surface of the host, and the penetrating tubes 
may have a shorter or longer course before they pierce the cells. 
Whether such appressoria have been forced away from the sur- 
face of the leaves by the resistance offered to the elongating 
penetrating tubes by the epidermis is not known. 
It might be supposed that, where an intercellular space 
occurs between two subepidermal cells, the penetrating tube 
might find its way into the interior of the leaf. The haustoria 
of Uncinula, however, have not been found deeper than the 
subepidermal cells. 
PHYLLACTINIA. 
Palla (24, p. 68) has recently reported that Phyllactinia® has 
the very interesting habit of sending nutrient hyphe through 
the stomata into the intercellular spaces of the infested leaves. 
Haustoria are thus constructed entirely on the interior of the 
leaf? and are not found in the epidermal cells as in Erysiphe. 
Because of this unusual habit Palla suggests the separation of 
the powdery-mildews into two families, the Erysiphez and the 
Phyllactinee. Upon the ground of certain differences, chiefly 
in the appendages of the perithecia, he gives (p. 65) the name 
P. Berberidis to the fungus on Berberis, as contrasted with P. 
suffulta on leaves of Corylus Avellana. No effort has been made 
to compare the material collected for this investigation with 
Palla’s results for systematic purposes, but the writer can con- 
firm most “of Palla’s observations on the intercellular hyphe 
and haustoria. Palla finds that the haustoria on the intercellular 
hyphe are found in the mesophyll cells in the two hosts he 
examined. As shown from a study of several hosts, Corylus, 
®It seems worthy of mention that, on mature perithecia, the appendages in this 
genus do not extend parallel to the surface of the leaf, as in the young stages, but 
obliquely downward. The result is that the perithecia are raised into the air for the 
length of the appendages. The perithecia, therefore, fall off easily when the leaves 
are handled. It may be that the appendages serve the fungus as organs of distribu- 
tion, 
7Investigators who have thought of the Erysiphez as purely epiphytic parasites, 
or as receiving their nutriment entirely from the epidermal cells, have been cited on 
P- 172. See also 27, 29, 31. 
