38 
ALBAN STEWART 
also found in a peripheral direction, as a larger sector of the stem is involved 
where the tissue disturbances are deepest than at the upper and lower parts 
of the gall. This fact is well shown in figure 8, where the inner parts of 
the bundles are normal. The statements just made are especially true for 
galls that are fusiform in shape but less true for those which are knot-like, 
because in galls of the latter type the disturbance is general throughout the 
greater part of the circumference of the stem. 
As a usual thing the cells composing the xylem have an upright position, 
but occasionally there are cells or groups of cells which are turned over at 
right angles to their normal position. As was stated earlier in this article, 
the cambium takes a more wavy course than in the normal stem. This 
is due to the fact that the central portions of the stem bundles grow more 
rapidly in the radial direction than do the flanks of the bundles, so that the 
cambium is bowed outward opposite the central portions (fig. 8). The 
leaf trace bundles, on the other hand, are often inhibited in their growth 
and the cambium opposite them extends inward farther than in normal 
stems. Sometimes the cambium is obliterated for a space, or at least there 
are no cells which have the form of cambium cells. In cases of this kind 
it is difficult to find a separation between wood and bark. 
The normal phloem (fig. 6) has both sieve tubes and companion cells 
well marked. Where abnormalities are great in the gall all distinction 
between sieve tubes and companion cells is lost and the cells have increased 
enormously in size. Figure 7 was drawn from such tissue and is on the 
same scale as figure 6. The cambium is towards the lower side in figure 7, 
and shows the rapid increase in the size of the cells after they are formed. 
The phloem is here composed of undifferentiated parenchyma which has 
lost all the characteristics of phloem ^ells. In longitudinal sections through 
the phloem there are no indications of sieve plates and the individual cells 
are about isodiametric. In cases in which the bundles have become in- 
fected rather late in their growth there is a mass of normal phloem next 
the bundles of bast fibers, w^hile that next the cambium is similar in structure 
to that shown in figure 7. 
In the normal stem a bundle of bast fibers usually occurs opposite each 
fibrovascular bundle. In the gall this is not always true, group of paren- 
chyma cells replacing the bast of fibers. Sometimes in such places the 
bast fibers are imperfectly formed, in that the walls are thinner and less 
regular in shape and they still contain protoplasm. These cells are often 
scattered about through the inner bark and are not arranged in well defined 
bundles as is the case with normal bast fibers. Well formed fibers some- 
times occur among the abnormal ones. 
The cortical portion of the bark is usually not greatly changed and as a 
rule there are but few sporanges in it. The cells often become lengthened 
tangentially and cross walls form in many of them but otherwise there is no 
great change. Where the bark has been torn open by pressure from within 
