HEMIPTERA. 
159 
the species is provided for. This winged form also con¬ 
sists entirely of females, and is known as the winged agamic 
. form. They produce in turn the wingless agamic form, a 
single, winged individual, which has flown to a new plant, 
starting a new colony. Generally on the setting in of cold 
weather, or in some cases on the failure of nourishment, 
the weather being still warm, there is produced a generation 
including individuals of both sexes. These are known as 
the sexual forms. The males may be either winged or 
wingless, but these true females are always wingless. The 
sexual forms pair, and the female produces one or more 
eggs. It is in this state that the species usually pass 
the winter, and consequently these eggs produced by the 
sexual form are often called the winter eggs, to distinguish 
them from eggs produced by the agamic forms of certain 
species, and which are incorrectly termed pseudova (pseu¬ 
do' va). From the winter egg there hatches, usually in the 
spring, an agamic female, which, as she is the stock from 
which the summer generations spring, is often called the 
stem-mother. The peculiar reproduction of the agamic 
forms is often termed reproduction by budding. 
Plant-lice are often very destructive to vegetation. The 
ordinary methods of combating them are either by the use 
of a strong solution of soap or with kerosene emulsion. 
Plant-lice vary greatly in their habits. Certain species 
live in the ground on the roots of plants. The Lettuce 
Earth-louse, Rhizobius laetucce (Rhi-zo'bi-us lac-tu'cae), is a 
good illustration. This occurs on the roots of lettuce, often in 
great numbers. Other species are found on the roots of grasses 
or herbaceous plants and usually accompanied by ants. 
On the other hand, many species, in fact the majority of 
Aphids, pass their lives on the foliage of plants, infesting 
especially the tenderer leaves. Familiar examples are the 
Cabbage Aphis, Aphis brassicce (A'phis bras'si-cae), the Apple- 
tree Aphis, Aphis mali, the Cherry tree Aphis, Mysus cerasi 
(My'sus cer'a-si), and the Peach-tree Aphis, Mysus persicce 
