348 
HARRY R. ROSEN 
sucking out the contents and a consequent decrease in size of the 
portion attacked? This seems the most reasonable explanation. 
Although a few of the upper epidermal and mesophyll cells are killed 
(I have never found more than two or three epidermal and two meso- 
phyll cells killed), by the action of the proboscis, the hollow is not the 
result of their death and a subsequent sinking in of the neighboring 
tissue. 
Employing the technique used by Barber (2 and 3), a considerable 
number of fine, capillary glass tubes were made measuring from 5 to 
20 fjL in diameter and around 0.5 mm., in length. About 25 of these 
tubes were stuck into very young vine leaves and allowed to remain 
there until the leaves had grown to a fair size. Several punctures in 
small leaf areas were made in some cases and a circle of india ink was 
drawn around each area to indicate the place of operation. Young 
leaves punctured in this manner were also permitted to grow to a fair 
size. Sections were then made of the wounded leaf areas, and while 
microscopic examination showed dead cells in the punctured regions, 
no depressions were found around the point of injury. These ex- 
periments add weight to the belief that the depression in the vine leaf 
below the insect is not due simply to a puncturing by the insect's 
proboscis. Furthermore, in figure 9, it is seen that there is a depres- 
sion not only of the upper leaf tissue but also of the lower, where the 
proboscis has not gone through and has not killed any of the lower 
epidermal cells. 
It occurred to the writer that the force exerted by the insect's 
body pushing against, and weighing down upon a delicate, embryonic 
leaf, might have something to do with the formation of the depression. 
The furrows made by twiners on growing plants would perhaps be an 
example of the effect of such a force. Moreover Molliard (21) has 
noted the fact that a pressure exerted upon the surface of a growing 
portion of a plant may cause a depression at the point of contact, and 
an increase in growth, a hyperplasia, in portions adjoining the de- 
pression. 
To test the effect of a force comparable to that exerted by the body 
of the insect, fine glass needle points, made in the same manner as 
those described above, measuring 5 to 20 microns in thickness and 
several millimeters in length, were held over a very small flame, so 
that the heated end coiled up and consolidated into a small glass 
knob. The tubes thus treated appeared as very small, round-headed. 
