PLANT LICE. 163 
covering of the roots and to greater natural vigor. All our 
vines are not equally resistant, and no vines are wholly im- 
mune, while several of our cultivated varieties, as the Delaware, 
are almost as defenseless as European vines. Of the many wild 
American vines, those of chief importance as sources of stock 
are the Aestivalis, Riparia, and Labrusca. Of these, Aestivalis 
and its cultivated varieties rank first in resistant qualities. The 
varieties of this species commonly grown ‘and used for stocks 
are Herbemont and Cunningham. These are also very valuable 
on account of the superior quality of their own fruit. 
“The wild varieties of Riparia are quite resistant to the root 
louse, although the most subject of all vines to the attacks of 
the leaf-gall lice. Of the cultivated varieties the Clinton, the 
Taylor, Solonis, etc., are very commonly used as stocks. The 
fox grapes, derived from Vitis labrusca, while more resistant than 
European grapes, are much inferior to the other American species 
mentioned in this respect. Isabella and Catawba, for example, 
are very subject to root lice; the Concord, while not often seri- 
ously injured, is still rather subject to attack and therefore not 
so valuable as a source of resistant stocks. There are many 
hybrids of these and other American species, which are used 
either direct for their fruit or as stocks. Conditions of climate 
and soil will determine the particular variety to be employed, and 
these points can only be settled by experimental tests for new 
localities.”’ 
Other species of phylloxera are found in galls on the leaves 
of various plants, but chiefly those of the hickory, while a few 
occur on the oak and chestnut, and even in the deserted and 
empty galls found so often on the cottonwood. 
SUB-FAMILY PEMPHIGINA. 
(Gall-making Plant-lice). 
The insects forming this sub-family are distinguished by 
having three discoidal veins on their front wings; the third 
discoidal vein has only one fork or is simple; the honey-tubes 
are either wanting or are tuberculiform. 
The lice belonging here live mostly above ground, although 
there are also some root-inhabiting forms; some are remarkable 
