1gtt] OVERTON—TRANSPIRATION AND SAP-FLOW 59 - 
but left connected with the roots. A section of the stem 10 cm. 
long of one of two similar cut plants whose daily water loss was 
5.4 gm. was immersed for 20 minutes in hot wax, which was allowed 
to cool about the stem. This plant gave off 5.6 gm. of water dur- 
ing the next period of 24 hours, an actual increase over the amount 
given off before treatment; the control gave off 5 gm. during the 
same period. During the third period the plant with the dead 
section of stem gave off 1.8 gm. of water, and the control 2 gm. 
It seems evident from these results that steam has. the same effect 
on the transpiration of cut stems set in water that it does on normal 
plants. 
Judging from the behavior of the leaves on a stem with a steamed 
section, from the collapse of the mesophyll cells, and from the 
apparent disorganization induced by steaming as indicated by the 
plugging of the water passages, I have been led to conclude that 
this method of killing the cells is not a satisfactory one in order to 
settle the question as to the relation of living cells to sap-flow. I 
agree with Czapexk that the killing of the cells should be accom- 
plished without further disorganization of the transpiring tissues. 
I have tried, therefore, to find a more satisfactory method of killing 
the cells of the stem without causing so much disturbance and dis- 
organization as is induced by steam. I have surrounded the stem 
in the region to be killed with hot paraffin or wax, by pouring it into 
the incasing glass tube at a temperature of 110° C. and allowing 
it to cool and set about the stem, thus killing it and protecting it 
during the experiment. In some cases I have found it necessary 
to protect the stem further with grafting wax. On microscopical 
examination I find that the portions thus treated are quite dead, the 
parenchyma cells having their protoplasts contracted, and the 
peripheral mesophyll cells being discolored, with their protoplasts 
contracted. No change could be observed in vascular bundles. In 
such stems when cut and set in eosin, the color passes up mainly 
in the tracheae, and does not diffuse laterally into the surrounding 
tissue as in steamed stems. I also find that much less plugging 
of the vessels above the killed portion occurs after this method, 
as well as less plasmolysis of the mesophyll cells. In every respect I 
think this method of applying heat is far superior to steaming, 
