318 BOTANICAL GAZETTE [OCTOBER 
water columns the incipient drying of the leaves should be increased, 
which should in turn lower the transpiring power. 
— The relatively high transpiring power indicated 
for the hours 14:30 and 15:30 appears to have 
2020 followed the breaking of the water columns, by 
which the entire water mass of the plant had pre- 
viously been united. Such a breaking should 
remove the tensile strain from the leaf cells 
decreasing the saturation deficit of their exposed 
_cell walls and increasing their transpiring power. 
From the time when this rupture occurred, the re- 
moval of water from the leaves should be accom- 
panied by air entrance and no further tensile 
strength could be developed. If this is the correct 
interpretation of the observation here set forth, 
the rupture of the water columns extended over the 
period from 13:30 to 15:30, during which time 
the transpiring power was markedly increasing. 
After hour 15:30, it is to be supposed that 
practically no more water entered the leaves from 
the stem, and the leaves gradually dried out, 
exhibiting the decreasing transpiring power which 
should accompany desiccation. 
2029 
% 
™~ 
Ba 
INI 216 
0699 _ 0657 bane 0899 
830 9:30 10:30 11:30 12:30 13:30 14:30 15:30 __ 163d 
s showing march of index of foliar transpiring power for wilting 
cailiaee ines lower leaf surface full line; upper leaf surface broken line. 
From the nature of permanent wilting, and from the theoretical 
considerations above stated, it appears highly probable that this 
