444 
[March 
the insect shifted its quarters to some other large trees which stood at 
the other end of the group, passing over a number of much smaller 
and younger trees lying in the intermediate space. One of these last 
large trees in particular was so badly infested by G^ni'ps in 1863, that 
it must have borne from 400 to 500 galls. I have, however, occasion¬ 
ally found these galls elsewhere on quite young trees and even on sap¬ 
lings. 
These same galls occur on the black oak in two or three other localities 
near Rock Island, Illinois, but by no means so abundantly. They are, 
however, exceedingly local, and if all the black oaks within two miles of 
Rock Island were divided into groups of the same size as the one above 
described, I am confident that for one such group where these galls 
exist, certainly fifty and perhaps one hundred will be entirely des¬ 
titute of them. I speak the more confidently on this point, because 
one of my favorite modes of collecting is by “ beating,” and because it 
is scarcely possible to “beat” an oak, where these large and conspicu¬ 
ous galls or “ oak-apples” exist, without becoming aware of their pre¬ 
sence. Another fact leads to the same conclusion. Every spring in 
the locality above referred to dozens and dozens of oak-apples of last 
year’s growth may still be seen hanging on the trees, being almost in¬ 
variably those from which the G^riips or its parasites have made their 
exit. In the winter of 1863-4 I have carefully looked for such oak- 
apples in many black oak patches where I had failed to find them in 
the summer, and could not discover a single one. Yet the trees be¬ 
ing mostly leafiess a single specimen would have been easily seen. On 
the same prairie mentioned above there is another group of black oaks, 
similar and similarly situated to the one that swarms with oak-apples, 
and distant from it about I mile. Yet a careful search in the winter 
failed to discover a single oak-apple hanging on the boughs. On the 
other hand I had no difficulty in finding on the same occasion many of 
these galls still hanging on the trees in the two or three localities where I 
commonly find them in small numbers in the summer; nor in finding nu¬ 
merous galls of Gynips, quercus inanis 0. S. on the red oak still hang¬ 
ing on the tree. Yet that gall is not one-twentieth part so abundant 
as the one which produces aciculata. 
There are found near Rock Island the following species of oak, 
named in the order of their relative abundance, and on none of them, 
