379] B. E. Livingston 181 
for last hour of incipient drying was 1.3 cc. Transpiration for this 
hour was 0.38 g., and absorption was 0.11 ce. 
(8) Dec. 1, cloudy. Mimosa plant, Transpiration was greater 
than absorption for the period 7:55 a. m. to 3:55 p. m., incipient 
drying amounting to 2.97 g. Absorption was greater than tran- 
spiration for the period 3:55 to 5:55 p. m., the plant gaining in 
weight 0.27 g. No wilting was noted; the leaves were in night 
position at end of last hour. Atmometric index for last hour of 
incipient drying was 0.7 cc. Transpiration for this hour was 1.03 g. 
and absorption was 0.87 ce. 
These data show very clearly that incipient drying, tempo- 
rary wilting, and even permanent wilting of most of the 
leaves, may occur without any resistance at all to water- 
absorption by roots. These phenomena are here quite inde- 
pendent of such resistance to water intake as may be offered 
by unsaturated soils. Furthermore, in the complete absence 
of environmental resistance to water absorption by the root 
system, incipient drying may begin with an evaporating 
power of the air as low as 0.33 cc. per hour from the Living- 
ston standard white sphere (Coleus, Nov. 4). Consequently, 
it does not require a high atmometric index to render the 
transpiration rate larger than the rate’ of absorption, in the 
case of some plants at least. The truth of this statement must 
be much more pronounced when the plant roots are sur- 
rounded by ordinary, fairly dry soils, which interpose an ex- 
ternal resistance to water intake. 
Unfortunately, atmometric observations were omitted in 
the first three tests, so that it is not possible to state what 
order of atmometric index values produced the wilting phe- 
nomena recorded for Sept. 20, 21 and 23. It is, of course, 
certain that these index values were not exceptionally high, 
however; the index for Baltimore is never high, and there 
was no artificial heat applied to the greenhouse on these 
days, so that the index value was not artificially raised. It 
is worth something to note that permanent wilting of most 
of the leaves of healthy buckwheat plants occurred in an 
unheated greenhouse in Baltimore on Sept. 20, with clear sky, 
and on Sept. 23, with partly cloudy sky. 
