376 
Indiana University Studies 
In the earliest stage examined the gall was 2. mm. in diameter. 
At this time none of the cell walls are sclerenchymatous and the nutri- 
tive zone is only about four narrow cells in width. Outside of this 
layer is a part of the parenchyma zone in which each cell contains a 
large crystal mass. 
At a stage in which the gall is full grown but still soft, all the 
zones are differentiated. The epidermis is thrown into folds and is 
covered with a heavy cuticle [Cosens fig. 64]. This is absent in the 
sinuses of the folds and on the epidermis covering the spines. The 
parenchyma zone is gradually converted into a protective tissue of 
porous sclerenchyma. The thicker deposit is usually on the walls of 
the cells nearer the periphery of the gall. Along the outside of the 
nutritive zone and throughout the protective layer generally are lines 
of small cells almost square in outline. The walls of these cells are 
very thick and the lumen of each is filled with a single crystal or a 
mass of crystals. In galls that had become hard all the cells of the 
parenchyma zone were found to have sclerified. . . . 
The nutritive layer of this gall differs very little in appearance 
from the parenchyma zone. Its cells do not contain the rich protoplasmic 
contents common to the nutritive zones of typical Cynipid galls. 
Cook (1904, Ohio Nat. 4:142, fig. 125) gives this more brief 
but in some respects supplementary description of the struc- 
tures of the same gall : 
The galls are always developed on the mid-rib of the leaf, but con- 
tain no fibro-vascular bundles. The nutritive zone is thick and very 
rich in protoplasm. The protective zone is also thick and gradually 
merges into the parenchyma zone, which is also thick. The epidermal 
zone is very irregular and is covered with numerous unicellular tri- 
chomes. 
The differences which the two botanists found in the amount 
of protoplasm in the nutritive zones might be explained as 
differences in the state of development of the material with 
which they worked. Too often micro-morphologic studies ig- 
nore the fact that tissues and cells are not static structures 
to be studied whenever and wherever the botanist or zoologist 
cares to make his sections, but unstable living materials that 
change with age and under the stress of the multitudinous 
forces of both the external and internal environments. Both 
Cosens and Cook seem to have been biased in believing that all 
cynipid galls must have the same four layers that the earliest 
European students found in the first species they happened to 
have studied. My own interpretation of these Acraspis galls 
(see pp. 40 to 43) is that the nutritive layer is very poorly 
developed, the protective (sclerenchyma) zone is absent, that 
