452 BOTANICAL GAZETTE [JUNE 
and other tissues especially concerned with these processes are 
developed correspondingly. 
Passing from the leaves to the branches, comparison of cross- 
sections of branches bearing galled leaves with cross-sections of 
other branches bearing only normal leaves, reveals certain differ- 
ences. If one makes a series of cross-sections through succes- 
sive segments of one branch, the leaves of which have been 
attacked in successive years by the gall-fly, and a similar series 
of cross-sections through a branch which has borne only healthy 
leaves, we shall see that the growth of the branch in thickness 
each year is proportioned to the amount of galling which has 
taken place. The accompanying figures show this. In fig. z we 
1901 100 900 "1 96 1895 1894 
Fic, t. 
have part of a cross-section of a branch, the oldest wood in 
which was formed in 1894. The drawing is by Leitz drawing 
prism. I have known this tree and watched it constantly, 
beginning with the spring of 1898, the year when, according to 
entomologists, the attacks of the gall-fly were 
the worst. The fly first appeared in noticeable 
1902 numbers in 1896, and since 1900 it has been far 
less numerous than in the preceding five years. 
The narrow annual rings indicated in the above 
_ drawing coincide exactly with the most serious 
attacks of the gall-fly. . 
In fig. 2 we have a branch the oldest wood 
in which was found in 1900. The terminal bud 
of this branch had been injured shortly before I 
cut it, which was in March 1903, when I collected 
all the material here figured. On this branch I 
hates counted all the leaves still present, and the num- 
bers were as follows: 1 normal leaf still attached to the part 
of the branch begun in 1900, 40 galled and 26 normal leaves 
i 
1903 
