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before the adjoining cells have shrunken to any appreciable extent. 
Further the cells of these leaves do not enlarge to any appreciable 
extent, if the tension is removed entirely by cutting or tearing the 
leaf or if the tissue is macerated and the cells set free in water. 
The second hypothesis does not appear valid, since if such an 
enzyme were secreted it would probably spread to adjacent cells. 
Also it is not very likely that, with the loss of water from the adjacent 
cells and consequently to some extent from these, the internal pressure 
would be great enough to expand the cells very much. At least with 
only ordinary osmotic pressure to hold the cell water, the cells would 
quickly collapse on exposure to the air. 
The third hypothesis is similar to that held by Fischer (lo) to be 
the cause of oedema in animals, where the swelling is said to be due 
to modifications in the fibrin of the blood, muscle, etc. At first the 
disappearance of the plastids and nuclei seemed to argue in favor of 
this hypothesis, but when the stained sections were examined again 
the interior of the cells was found to be colorless while the protoplasm 
lining the cell wall was stained and distinct, which indicates that the 
interior is filled with cell sap. 
That osmotic pressure is capable of causing the enlargement of 
plant cells is shown by the development of intumescences under various 
conditions during which increased osmotic pressure in the cells occurs. 
The question is then, how can the increased pressure be brought about 
in this case. 
Production of Shot Holes Correlated with Amygdalin Content of 
Leaves, — Observations seem to indicate that the shedding of the dis- 
eased spots is correlated with the amygdalin content of the leaves. 
As before mentioned the spots are shed from P. virginiana during all 
the spring and early summer. Morse and Howard (20) have shown 
that the young leaves of this species are very rich in amygdalin which 
diminishes in amount with the age and vigor of the leaves. Of the 
species under observation, the following also shed the spots infected 
by Cylindrosporium while the leaves are young: P. serotina, P. penn- 
sylvanica, P. cerasus and less frequently P. domestica. They are never 
shed from leaves of P. mahaleb, P. spinosa (not seen infected while 
leaves were very young) and, except under rare conditions, from P. 
avium. According to publications summarized by Wehmer (30), 
amygdalin is found in the leaves of P. virginiana, P. pennsylvanica, 
P. serotina, P. cerasus (?) and in young but not in mature leaves of 
P. domestica. It is not found in P. mahaleb, P. spinosa, or P. avium. 
