IIo BOTANICAL GAZETTE [FEBRUARY 
experiments certainly suggests that the death of the stem cells 
does not operate in any direct fashion to cut off the water supply. 
Such a period as 18 days gives opportunity for the development 
of all sorts of secondary causes, to which the final death of the 
leaves may well be due. That the amount of water carried is at 
once reduced may just as well be due to gross mechanical changes 
secondarily produced in the tissues as to the death of the cells. 
Drxon calls attention to the fact that the investigators who first 
observed the withering of the leaves above a heated portion of the 
stem, such as WEBER (40) and JANsE (16), did not attribute the 
phenomenon simply to the lack of activity of the dead cells of the 
stem, but to a possible blocking of the vessels, which thus diminishes 
the water supply. It is certain from the methods which I have 
used to protect the steamed portions of the stems, that the dimin- 
ished water supply which reaches the leaves after treatment cannot 
be due to a lateral evaporation from the heated stretch. The care- 
fully sealed incasing glass tubes preclude such a_ possibility. 
Ursprunc has also concluded from his experiments that the wilting 
of the leaves above a killed portion of the stem is not due to 4 
lateral evaporation from the heated portion. 
In the experiments whose results are shown in tables VIII and 
TX, there was an increased amount of water transpired on certain 
days after a section of the stem was killed with heat. It appears, 
therefore, that UrspRUNG’s statement that the fading of the leaves 
above a killed portion is a sure index that insufficient water supply 
reaches them is not proven, and that the wilting may well be due 
to deleterious substances being introduced into them from the dead 
cells. Although the plant described in table [X had an increased 
amount of water ascending to the leaves, they finally withered 
while still giving off large quantities of water. I am forced to 
agree with Dixon (10-12) that UrspRUNG’s interpretation of these 
phenomena is an arbitrary one. As noted above, Drxon ascribes 
the earlier wilting of the leaves on stems, a section of which has been 
killed with heat, to a possible clogging of the vessels, which hinders 
water passage, or to a breaking of the water columns due to the 
heat used, which may thus interrupt the continuity of the flow. 
He holds, however, that the withering of the leaves is due chiefly 
