1915] BAKKE—PERMANENT WILTING Sif 
hours. Then a marked increase in the index values is evident, 
lasting for two hours, after which another decrease is clearly 
shown. 
| TABLE I 
MARCH OF THE INDEX OF TRANSPIRING POWER FOR UPPER, LOWER, AND ENTIRE LEAF 
SURFACE OF UPROOTED PLANT OF Helianthus annuus L. DURING PROGRESSIVE 
WILTING AND DRYING OF THE LEAVES 
INDEX OF FOLIAR TRANSPIRING POWER 
TIME OF ; 
OBSERVATION 
Lower surface | Upper surface | Entire surface 
SROs 0.9468 0.9020 0.9243 
coe (0 Me naers Maerae 0.1175 0.1289 0.1232 
T9530 005 Ov 0.1054 0.0865 0.0959 
132200 S250 (3, 0.0632 0.0699 0.0665 
pdr Wate co. De ae 0.0057 0.0616 0.0636 
E3580 2' 55 3s 0.0571 0.0578 0.0574 
FAs gO ees 0.1029 0.1013 0.1021 4 
eg ls ee 0.1723 0. 2029 0.1876 
160302354 0.0899 0.1216 0.1058 
To interpret these alterations in the index values, it may 
safely be supposed that the great initial fall in the graphs rep- 
resents the prompt increase in incipient drying’ within the 
leaves, which must have followed the uprooting of the plant and 
the consequent breaking of its connection with the soil moisture 
films. Temporary wilting had already set in before the end of 
the first hour. 
After wilting began, the increase in incipient drying apparently 
continued, but at a low rate, as indicated by the gradual down- 
ward slope of the graphs for the hours 9:30 to 13:30. During this 
time it may be supposed that the continuous water columns? of the 
plant remained mainly intact, so that the leaves were still slowly 
drawing water from the stem. With increasing tension on these 
7 Lrvincston, B. E., and Brown, W. H., Relation of the rad march of transpira- 
tion to variations in the water content of foliage leaves. Bot. GAz. 53: 305-330. I912. 
8 Brown, W. H., The relation of evaporation to — water content of ws soil at 
the time of wilting. Plant World 15:121-134. 1912; CALDWELL, J. S., loc 
beta tad _ H., Transpiration and the ascent of sap. Re Rei Bot. 3: 1-66. 
0., a. Beitrige zur Kenntnis der Wasserbewegung. 
REN 
Flor, 103: as. 
