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ALBAN STEWART 
A great reduction in the number, or an entire lack of vessels. 
7. A shortening of many of the cells of the wood. 
8. Absence of distinct annual rings of growth. 
9. A suggestion of the return of the cambium to normal activity 
after a time. 
10. Woody inclusions in the bark. 
The fact that similarities often exist between the structure of 
galls and traumatic tissue is well known among workers in patho- 
logical plant anatomy. Kiister (13) mentions this fact in several 
places in his work. Possibly one of the most noteworthy single ex- 
amples of this kind is that mentioned by Molliard (17, p. 200) in 
which by pinching the buds of Pelargonium zonale structures were 
produced similar to those in the flower galls on Geranium dissectum 
caused by Cecidophyes Schlechtendali. I believe, however, that this 
is the first time that the conditions in a single gall have been correlated 
with the conditions in traumatic tissue in so many important ways. 
The comparisons made with wound tissue in this article have been 
based largely upon the general results of De Vries and Maule. I 
hope, however, to continue further this investigation on other woody 
oak galls, and to compare more closely the structure of the gall wood 
with that of traumatic wood of the oak. 
Methods 
The galls used for sectioning in this work were preserved in a 
weak solution of formaldehyde when they were collected and left in 
it until they could be further treated. In order to prepare sections 
for study, the galls were first macerated to remove the formaldehyde, 
and were then placed under the receiver of an air-pump and the air 
exhausted until bubbles ceased to rise from them. They were then 
transferred to strong hydrofluoric acid and left for about two months 
in order to remove all of the mineral matter. No difficulty was 
experienced in cutting sections less than 10 in thickness except that 
large sections, cut thinner than this, were badly broken up in the 
subsequent handling. Sections 10 />i in thickness were used in most 
instances as they were found to be sufficiently thin for all that was 
required. 
An alcoholic solution of safranin was employed for staining, and 
as a counter stain "licht Griin" dissolved in clove oil was used. 
This had the double advantage of both counterstaining and clearing 
