NOTES ON THE ANATOMY OF PERIDERMIUM GALLS 1 7 
the arrangement of the tracheids is not strikingly different from 
normal (see plate I, figure i). Disturbance in the arrangement does 
occur sometimes in which the tracheids are usually turned over to 
right and left tangentially, probably indicating regions of ball-forma- 
tion of tracheids. Similar conditions occur in juniper stems infected 
with Gymnosporangium juniperinum according to Wornle (18, p. 83). 
The width of luminae and thickness of the walls of the tracheids does 
not differ greatly from that of normal cross sections except in the 
summer wood where the walls are much thinner than in normal summer 
wood (see plate I, figure i). This is quite different from the wood of 
Ahies halsamea infected with Peridermium elatinum, as Anderson (2, 
P- 337) has reported thicker walled tracheids than normal. There 
are but few layers of summer tracheids formed, and it is due to this 
fact that the rings of growth are sometimes not well defined. A 
similar condition may result in juniper stems infected with Gymno- 
sporangium juniperinum according to Wornle (I.e.). If cross sections 
are cut above or below the center of the gall they will usually show a 
structure between cross and tangential. This peculiar condition is 
due to the fact that the tracheids pursue a more or less horizontal 
course for some distance after they bend outward into the gall from 
the normal wood. 
In radial sections the course of the tiacheids follows in a general 
way the outer contour of the gall (text-figure ih). There are some 
exceptions, however, as a nearly true transverse structure may occur 
as well as wavy structure. In tangential sections the normal course 
of the tracheids is often very much disturbed, resulting in wavy struc- 
ture and balled or whorled arrangement. Large whorls, very complex 
in structure, sometimes occur in such sections (plate I, figure 2). 
According to Maule (11, p. 10) these seldom appear in other than 
tangential sections of traumatic wood. I have found this to be true 
in this gall and in the gall of Andricus punctatus on the black oak, see 
Stewart (17, p. 541). Small tracheid whorls occur in traumatic 
wood of the jack pine but I have failed so far to find any which ap- 
proach in any way the size of the one shown in figure 2. Large struc- 
tures of this kind do sometimes occur in traumatic pine wood, however, 
as Maule (I.e., p. 12) reports them from Pinus Pumilio. U- and 
Y-shaped tracheids are common in regions of extreme distortion in 
the gall. 
In addition to the fusiform rays, which are low and scattered in 
