THE FREE WATER OF THE SOIL. 207 
although there be no ascending aqueous current. (H. C. 
G., pp. 288 and 340.) 
In accordance with these views, vegetation grows as well 
in the confined atmosphere of green-houses or of Wardian 
Cases, where the air is for the most part or entirely satu- 
rated with vapor, so that transpiration is reduced to a mini- 
mum, as in the free air, where it may attain a maximum, 
‘As is well known, the growth of field crops and garden 
vegetables is often most rapid during damp and showery 
weather, when the transpiration must proceed with com- 
parative slowness. 
While the above considerations, together with the asser- 
tion of Knop, that leaves lose for the first half hour nearly 
the same quantities of water under similar exposure, 
whether they are attached to the stem or removed from 
it, whether entire or in fragments, would lead to the con- 
clusion that transpiration, which is so extremely variable 
in its amount, is, so to speak, an accident to the plant and 
not a process essential to its existence or welfare, there 
are, on the other hand, facts which appear to indicate the 
contrary. 
In certain experiments of Sachs, in which the roots of. 
a bean were situated in an atmosphere nearly saturated 
with aqueous vapor, the foliage being exposed to the air, 
although the plant continued for two months fresh and 
healthy to appearance, it remained entirely stationary in 
its development. (Ve. St., I, 237.) 
Knop also mentions incidentally (Vs. Sé, I, 192) that 
beans, lupines, and maize, die when the whole plant is 
kept confined in a vessel over water. 
It is not, however, improbable that the cessation of 
growth in the one case and the death of the plants in the 
other were due not so much to the checking of transpira- 
tion, which, as we have seen, is never entirely suppressed 
under these circumstances, as to the exhaustion of oxygen 
or the undue accumulation of carbonic acid in the narrow 
