1918] W ELLS—ZOOCECIDIA 539 
Slightly over half of the galls (53 per cent) occur on the leaf 
blade. This fact is of course related to the relatively large amount 
of embryonic leaf tissue exposed in the early stages of shoot develop- 
ment. In the cases of the stem, root, and bud galls numerous 
factors enter, but perhaps the most important is the factor of insect 
equipment necessary to place the larval cecidozoon in contact with 
the meristematic tissues. 
Some figures pertaining to gall structure were obtained which 
are of interest. A few words of explanation are necessary before 
presenting the tabulation. Under the monothalamous galls were 
included those types which, so far as could be determined, are 
generally one-chambered, that is, the gall never is a structure 
constantly characterized by the confluence of the walls of two or 
more chambers as in the polythalamous condition. A few species 
are intermediate and were classified in the direction in which it was 
believed they leaned the more strongly. A number of galls, such 
as the erineum (hypertrophied epidermal cells) types, do not fall 
in either of the above categories and cannot be included in such a 
classification. 
In those cases in which sufficient data were available, an attempt 
was made to study the galls on the basis of KUster’s division of 
cecidia into kataplasmas and prosoplasmas. By “kataplasmas 
KUsTEer means those indefinite, indeterminate galls whose structure 
is developed through hyperplasia of embryonic tissue, the end 
product not becoming in its differentiation, orientation, and form 
of tissues fundamentally different from the normal plant part. 
“Prosoplasmas,’’ on the other hand, are highly definite and deter- 
minate galls whose structure differs fundamentally from the normal 
plant, the tissues in their form and orientation characters con- 
stituting an aggregation of new qualities. These two groups 
intergrade, but the intergrading forms are relatively few in number 
and were classified according to what was believed to be the 
predominating condition. In all cases where data were not suffi- 
cient to pass judgment, the gall was omitted from the census. 
Another set of figures presented is that based on KisTER’s 
classification of galls into organoid and histoid types. An 
“organoid”’ gall is one in which an entire plant organ (leaf, stem, 
