Ig1t] OVERTON—TRANSPIRATION AND SAP-FLOW 63 
to be noted that after the second day the amount falls from 1.5 
gm. to o.g gm., after which there is a more gradual daily dimi- 
nution in the amount transpired. This seems to indicate, in the 
light of SCHROEDER’s results, that the leaves were dying, which 
is undoubtedly the case. Death is probably due to deleterious 
substances being introduced into the leaves from the killed portion 
of the stem. Examining table IX, in which the results are shown 
after using hot wax as a killing medium, we see that on the second 
day the plant increases the amount of water given off, which proves 
that it is not dying. There is also an increase on the fifth day over 
the fourth. I suspect that the leaves in this case have not been 
so severely poisoned as in the plant killed with steam. 
That withering of the leaves on stems, which have been killed 
with heat, is not due to lack of water, but to the toxic actioa of 
substances which have been carried to the leaves, seems to be 
shown by the above-described experiments. The fact that the 
longer the heated region, the more rapid the leaves wither, seems 
to favor such a view. That leaves above a steamed or otherwise 
heated portion do not wither in the same way as those simply 
deprived of water, but often discolor before shriveling, also sup- 
ports such a conclusion, as Drxon has already shown. 
Histological examination of such leaves shows that the proto- 
plasts and chloroplasts resemble those under diseased conditions 
more than those in leaves which are merely drying for lack of water 
supply. I agree with Drxon that leaves on cut branches die from 
lack of water supply, while in the case of leaves borne above a 
heated portion of the stem, they die because they dry. _ 
THE UNIVERSITY OF WISCONSIN 
Mapison 
