PLANT LICE. 147 
“From the above generalizations it will be seen that a single 
species of plant-louse may present three distinct forms; first, a 
sedentary, agamic, wingless form, furnished with mouth-parts ; 
second, a migrating, agamic form, which is winged and furnished 
with mouth-parts; third, a sexual form, of which the females 
are wingless, while the males my be either winged or wingless; 
in certain cases, at least, the sexual forms are mouthless. 
Fic. 135—Cockscomb gall on elm (Colopha ulmicola:) a, leaf showing galls from 
above and beneath—natural size; b, impregnated egg surrounded by skin of 
true female; c, newly-born young of second generation, ventral view; 4, its an- 
tenna; d, pupa of same, dorsal view; e, winged female; f, her antenna; g, an- 
tenna of stem-mother—all enlarged. After Riley and Monell in U.S. Geol. and 
Geogr. Survey. 
“There is unfortunately a generalization in most of the text- 
books on entomology, that is incorrect. It is that the winged 
generation is produced only on the approach of cold weather, 
and that this generation is the sexual one. 
“Plant lice are often very destructive to vegetation; they 
appear, however, to be more liable to attack unhealthy plants than 
those that are in good condition. The best method of destroying 
these pests is by spraying with a strong solution of soap, or with 
kerosene-emulsion. As plant-lice draw their nourishment from 
