Ig1t| OV ERTON—TRANSPIRATION AND SAP-FLOW II3 
plants in nutrient solutions containing a decoction. As noted 
above, the plants grown in such solutions began to droop in 3-5 
days, showing discoloration and fading along the veins in 7-8 days, 
while control plants grown in nutrient solutions without the decoc- 
tion remain perfectly normal. Drxon’s experiment, in which 
leaves normally supplied with water together with water from 
a heated side branch were shown to soon wither, seems to me 
quite decisive proof that deleterious substances enter the leaves 
from the killed portion. Ursprune (35-37), however, was unable 
to produce the same effect on the leaves of Impatiens by using 
Drxon’s method. 
Microscopical examination of the leaves from a stem killed by 
heat show in certain regions a discoloration of the mesophyll cells, 
the protoplasts being contracted and the chloroplasts being dis- 
colored. The leaves of plants grown in decoctions also show similar 
conditions. Drxon (10-12) also found disorganization and discolor- 
ation of the mesophyll cells of the leaves above a killed portion, and, 
as noted, even on a separate branch if some of its water supply passes 
through a heated region. In these cases it certainly appears that the 
leaves are drying not so much for lack of water as from injury and 
death of the cells. The observation of SCHROEDER (27) that most 
leaves can lose 50 per cent of their fresh weight without injury is fur- 
ther proof that leaves above a heated portion of a stem do not wither 
on account of the diminished water supply. In the microscopical 
examinations which I have made of leaves from steamed stems, 
I have found many of the conditions described by SCHROEDER in 
his studies on the symptoms of death as a result of wilting, namely, 
the contraction of the protoplasts of the mesophyll, and the change 
in color and rounding up of the chloroplasts. The fact that the 
plant killed with steam constantly decreases in the amount of 
water given off is also in harmony with SCHROEDER’s observations. 
The first 50 per cent of the leaf’s fresh weight is very rapidly lost 
when dying, as he shows, after which the amount lost decreases 
uniformly. My experiments, in which the amount of transpiration 
was determined after killing a portion of the stem with steam, 
show that there is in the first 2 or 3 days a very rapid and immediate 
decrease in the water loss, and that then the rate of transpiration 
