214 BOTANICAL GAZETTE [SEPTEMBER 
from the tip of the stem; two or three galls occasionally are spaced 
along a branch and separated by sections of normal stem, as shown 
in text fig. 2. The gall, especially when of the terminal type, bears 
a remote resemblance to a head of wheat. It is produced bya very 
marked shortening of the stem of the host, accompanied by a 
decided increase in its diameter. The contraction of the infected 
3 4 
Fics. 3, 4.—Fig. 3, Gall produced by Rhabdophaga strobiloides Walsh on Salix cor- 
data Muhl.; fig. 4, Gall of Phytophaga rigidae O.S. on Salix discolor Muhl. 
stem is so pronounced that the lateral buds, which would normally 
occupy 25-30 cm. of the stem, are crowded into a space of 4-5 cm. 
As the characteristic alignment of the lateral buds is approximately 
maintained on the abnormal part of the stem, there are 5 fairly well 
defined rows of buds on the gall. In each of these buds a larval 
chamber is located. 
Practically the entire pith and the cortex of this gall are com- 
posed of aeriferous tissue. It is absent only immediately around 
the zonal areas of the larval chambers, and in these regions it can 
be seen to have been obliterated by compression. The tissue is of 
