1918] BAKKE—WILTING 93 
older leaves (Ia,) is 0.59 and for the younger leaves is 0.67. The 
differences then in the order given are 0.33 ando.34. The respec- 
tive values on the 15th hour are 0.91 and 0.93. These give 
recovery value differences of 0.32 and 0.26. The drop in the 
afternoon reading is not a new thing, either in foliar transpiring 
power or in transpiration. No doubt this great resistance to the 
E ? 
lez x 4 
1 000 Pa NY 
938 f aN 
875 ; a ‘ 
a3 ps A j 
7508, y ms , 
P \ INOEX OF FOLIAR TRANSPIRING POWER Mg 
esd \ / 
\ ane, F 
A tare x h.o7 yi es 
af ow ‘at - 
563 emia | 
sod ee oa 
434 
376) 
313 
2 oof 250 
sy 
nso} 1881 F 
hoo} 125) cunuanes eer 
ee BEZe 
— ~ 2 a ~ e S Li T 1 Tt t J 
wy2ha916 
Fic. 2 
Passage of water is a condition of incipient drying. It may be that 
at this period, usually present at about the time of greatest evapora- 
tion, there is a lack of water, not only in the cells of the leaf, but 
also in the vessels themselves. SHREVE (40) has submitted evi- 
dence, at least theoretical, showing that variations in the tran- 
spiring power are due to variations in the water-holding capacity 
of the internal tissue. Using the Drxon (16, 17, 18) conception 
of continuous columns, as well as the results of the experiments of 
RENNER (34, 35, 36) upon transpiration, there is doubtless a greater 
tension present upon the water columns. If this is related to 
