Kinsey: Gall Wasp Genus Cynips 
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sorption by the other plant tissues) to a thin, broken layer of shrunken, 
partially empty cells. Poorly developed in any but the very youngest 
galls of Acraspis. Possibly directly descended from phloem. 
2. Protective layer. A sclerified tissue that is best developed in 
the European sub-genus of Cynips. The cell walls are thickened, and 
the cells may contain crystalline materials. The larval cell wall of most 
cynipid galls is largely made up of protective layer to which the rem- 
nants of the nutritive layer are attached on the inside and some spongy 
parenchyma tissue on the outside. The protective layer may be a direct 
development from sclerenchyma tissue in the vein. Apparently absent 
in Acraspis. 
3. Spongy parenchyma. Occupying the central portion and con- 
stituting the major material in all the spongy and more hollow oak 
apple galls of this genus. Poorly developed in the subgenus Antron and 
absent, as far as I can see, from the galls of the subgenus Acraspis. 
4. Collenchyma. Lying directly beneath the epidermis. A second 
layer in which the cells have thickened walls and usually crystalline con- 
tents. The layer appears hard and compact-crystalline to the naked eye. 
Practically absent (by an unfortunate coincidence) from the three species 
on which the first European studies were based, but present in most 
other species of that subgenus and in the other subgenera of Cynips. 
Constituting the bulk of the material in the galls of the subgenus Acras- 
pis, and well-developed as the compact outer layer of Antron. Cook 
(1904) and Cosens (1914) treated this layer in certain species of Acras- 
pis as modified parenchyma, but this seems to be an attempt to maintain 
the four layers of the European workers. This collenchyma layer in the 
gall may be developed from collenchyma to be found in a similar posi- 
tion in the normal leaf. 
5. Epidermal layer. The outer covering of the gall, including the 
fairly normal epidermis and all of the abnormal developments from it. 
Largely naked or at the most with stellate hairs in most groups of 
Cynips. With a peculiarly faceted surface in many species of Acraspis , 
in some cases with each facet terminated by a unicellular process which 
may be spiny or long and wool-like. Obviously a modification of the 
normal leaf epidermis. 
The precise homologies of these tissues must be made by some bota- 
nist using modern technic. It will be interesting to compare structures 
in galls of some of the species which occur either on upper and under 
surfaces of leaves, on veins, petioles, and (as in heldae) on young stems. 
The distribution of the five types of gal] tissues among the 
species of Cynips may be summarized as follows : 
