860 THE AMERICAN NATURALIST.  [Vor. XXXIX. 
THE CONE GALLS. - 
As is well known, a gall is some abnormal growth of a plant 
tissue resulting from an external stimulus. In the case of the 
cone galls and of the other bud galls of the willow the stimulus 
is furnished by the gall gnat. Whether it is given by the inser- 
| tion of the ovipositor into the bud, by the presence of the egg, 
or by the larvae, I cannot say. The gall attains its full growth 
by midsummer thus giving evidence of considerable stimulation. 
Regularity and symmetry in the shape of the gall can be 
accounted for by the stimulus, whatever it may be, acting 
equally in every direction. 
As a result of this stimulus, the bud takes on a remarkable 

C p C wW * r 
Fic. 1.— Cone gall of Salix. a,5, c, Salicis g phaloides (st 
d, Salieis strobiliscus ; e, f, Salicis strobiloides. 
k of stem): 

activity in growth, and develops a large number (60-75) of 
scales. These scales are placed in regular order, with their 
edges overlapping, and form in the center an elongate cell. 
This cell, protected by the numerous layers of scales, is the 
abiding place of the gall maker during its larval and pupal 
stages. 
