1gtt] OVERTON—TRANSPIRATION AND SAP-FLOW TES: 
whole plant, and that in many cases the new rate far exceeds the 
normal transpiration of a plant of the same age and superficial area 
under the same conditions. In these cases it is plain that the tissues 
are ruptured so as to expose additional cell surfaces to the atmos- 
phere. 
_ Drxon and Jory (13) consider that capillarity or imbibition of 
the mesophyll cell walls sets up a suction, aiding the osmotic suction 
in extracting water from the adjacent vessels. In the case of the 
poisoned leaves of Cyperus there can be no osmotic action of the 
cells. The imbibitional action of the cell walls, as conceived by 
Dixon, may however still keep the walls wetted, and the suction 
from the evaporation may be transmitted to the cohering water 
columns of the vessels. Drxon (11) points out that the point of 
support for the tensile strength in the case of transpiring dead 
organs is always the walls. He thinks that the presence of soluble 
substances on the outer surface of the walls would function also 
in maintaining the suction. Perhaps the condensation of the 
metallic salts of these poisons on the outer surfaces of the cell 
walls act in this manner. 
Boerum (4) formulated a theory of sap-flow based entirely upon 
capillarity, maintaining that the capillary attraction between the 
walls of the conducting tracts and the water is greater than 
obtains in a glass tube of the same diameter. The experiments 
of STRASBURGER (30), however, show that in the vessels of Aris- 
tolochia the capillary ascent of water is much slower than in glass 
tubes of the same diameter. It seems quite possible that HgCL, 
and some of the other poisons used by me, which cause-an increased 
amount of evaporation, as is shown in tables X and XI, may in 
some way alter this capillary relation so that the water may flow 
faster in such poisoned tubes. Cells without turgor, that is 
perfectly dead cells of the leaves, are able to raise water to a con- 
siderable height. STrRasBURGER showed that rather tall trees 
with poisoned leaves are able to raise water 22 m. ASKENASY (1) 
found that cut branches of Taxus and Viburnum, whose lengths he 
does not mention, which had lain for a long time in boiling water 
or in alcohol and were completely dead, could suck up water and 
eosin. Bornm (4, 5) also showed that water could rise in a dead 
