620 



THE STUDY OF INSECTS. 



States is a bullet-like gall, which is attached to the small 

 twigs, and which measures from one half to two thirds inch 

 in diameter. In this gall the central kernel is surrounded 

 by a hard, woody substance. 



The Giant Oak-gall, Andricus californicus (An'dri-cus 

 cal-i-for'ni-cus. — This is the most common oak-gall of the 

 Pacific coast. It is very abundant on the twigs and branches 

 of the California white oak, and during the winter, when the 

 trees are bare, it is a very conspicuous object. It differs 

 from the preceding galls in being of the type termed poly- 

 thalamous; that is, instead of containing a single cell, there 

 are several cells within it, in each of which a gall-fly is devel- 

 oped. This gall varies greatly in form and size ; some of the 

 larger ones measure ten or twelve inches in their greatest 

 circumference. The outer surface of the gall is white, and 

 usually smooth. 



The Pithy Blackberry-gall, Diastrophus nebulosus (Di-as'- 



tro-phus neb- 

 u-lo'sus), is 

 another exam- 

 ple of a poly- 

 thalamous gall. 

 It is a large 

 woody growth, 

 which occurs 

 on the stems 

 of blackberry. 

 It is sometimes 

 three inches in 

 length and one 

 and one-half 

 inches in diam- 

 eter. It varies 

 in shape, but 



Fig, 747. — The Mossy Rose-gall, Rkodites roses. there are 3.1- 



ways several wrinkled ridges along the stem. 



