656 
J. DAVIDSOX. 
America. Buckton (1880, p. 91) refers to Dr. Asa Fitch and 
Prof. Cyrus Thomas as refuting the idea of an American 
origin for woolly aphis, and also refers to Serville and Amyot 
as stating that it probably came to Europe through England, 
from America. 
Owing to the transportation of nursery stock woolly aphis 
has been carried from one country to another, so that it is 
now established practically wherever the apple is cultivated. 
Plant lice live on juices drawn from the tissues of growing 
plants, and in accordance with the sucking habits, the mouth 
parts, as is common amongst Hemiptera, are modified to 
form piercing and sucking tubes. 
Schizoneura lanigera attacks practically all varieties of 
apple trees in Britain, producing galls on the roots and 
branches. It is very destructive to nursery stock and young 
trees. According to Theobald (1909, p. 144), who cites 
French (1904) and Lounsbury, apples grafted on certain 
stocks, particularly the Majentin and Northern Spy, do not 
suffer from the root form. 
Howevei’, so much has been written about the habits of 
woolly aphis that it is, perhaps, unnecessary to say much on 
the point here. 
Although the damage done by S. lanigera on the roots 
and shoots of apple trees, resulting in the formation of gall- 
like growths, is familiar to economic entomologists, there 
appears some doubt as to the exact way in which the galls are 
produced. Riley (1879), discussing this point with reference 
to Phylloxera, refers to the work of Maxime Cornu (1878), 
Etudes sur le Phylloxera vastatrix,” who accounts for 
the swellings caused on the vine by P. vastatrix as purely due 
to the piercing action of the mouth parts, and the subsequent 
absorption of the sap from the wounds thus formed. There 
are manj^ aphids however, which, having fully developed 
mouth parts, do not cause galls to develop on the plant host. 
Some other factor must, therefore, be considered. As Riley 
(‘ Science’, 1895, N.s., i, p. 457) points out in the case of the 
larvte of gall-flies (Cynipidm), it is very probable that in 
