122 Canadian Record of Science. 
and the younger and more active these organs are, the 
greater will be the volume of water transpired within a 
given time. Upon the same principle, plants exposing 
large leaf areas, which retain their activity for a long time, 
are much more energetic agents in effecting this transfer 
and conversion than those which are more woody, have a 
less proportional leaf area, and mature earlier. 
Various investigations have from time to time been made, 
to determine the actual amounts transpired under different 
conditions. It will answer our present purpose to cite only 
one or two of these results. Héhnel records that in an 
old beech forest somewhat more than 100 years of age, the 
whole volume of water transpired by one hectare or 2.47 
acres, during the six months from June 1st to December 
Ist, amounted to between 2,400,000 and 3,500,000 kilos, or 
from 5,291,000 to 7,716,100 pounds, which, reduced to 
liquid measure, would give from 529,104 to 771,610 gal- 
lons. But these figures express only a portion of the water 
actually withdrawn from the soil, whence we can readily 
understand that plants serve as a drainage system as it 
were, for the soil. 
This fact has of recent years, been somewhat largely 
taken advantage of, for the purpose of draining swamp 
lands with a view to improving them for purposes of til- 
lage, and to remove their influence in promoting the 
dissemination of malarial organisms which are formed in 
the presence of large quantities of decomposing organic 
matter. For this purpose such plants as the sunflower, 
with its great expanse of leaf area, from which transpira- 
tion may proceed at a rapid rate, may be used. But the 
Eucalyptus globulus, or the blue gum of Australia, appears 
to answer this purpose even more fully, and is at the present 
time largely employed. 
The liberation of large volumes of water by a forest, as 
indicated above, necessarily tends to reduce the tempera- 
ture of the surrounding air and to bring it nearer the point 
of saturation—.e., it increases the relative humidity of the 
atmosphere, Any general influence which tends to still 
