Lvfluence of Climate on Cultivation. 
483 
have the power of taking up food from the soil in far greater 
quantity than is soluble in the water which merely evaporates 
through their leaves. The rapidity of growth in plants, it is 
certain, is by no means in proportion to the amount of water that 
they transpire, but often the reverse. It must be borne in mind 
that plants grow rapidly in close greenhouses or Ward's cases, 
where there is comparatively little transpiration by the leaves. 
These instances, as Professor Johnston, Yale College, Connec- 
ticut, observes, demonstrate that there is little connection between 
the amount of water exhaled and the quantity of matters absorbed 
by vegetation. 
We need not enter further upon this interesting question. 
Many unresolved problems in agriculture are however, as it 
appears to us, bound up in its full elucidation, to which it 
would be out of place at present to advert. It is only with that 
branch of the subject relating to the exact nature of the agents 
which influence the growth of plants under different climatic con- 
ditions that we have to do. If, however, for the sake of argument, 
we assume that the quantity of food taken up by plants from the 
soil is not in proportion to the amount of water which they eva- 
porate from their leaves, it puts us in possession of a simple and 
consistent means of explaining certain habits of plants. Rye, in 
this view, partly derives its power of growing in loose sandy 
soils from its evaporating less water than other cereals. This 
supposition, as already observed, implies the existence of a power 
residing in the rootlets of plants, whereby they exercise a solvent 
action on those substances within the soil which constitute their 
food. Hence we assume that plants, whose physiological struc- 
ture is otherwise similar, have the power of resisting drought in 
the inverse ratio to the amount of water they transpire by their 
leaves. 
The freer growth of the rye plant than of other cereals under 
certain atmospheric conditions has, perhaps, much to do with its 
greater power of resisting the exhalation of water from its leaves. 
Rye is sown for feeding sheep early in the spring in the south of 
England, but it is almost a worthless plant for this purpose in 
Scotland. The temperature during the day in the south is com- 
paratively high, which has the effect of stimulating its vegetative 
powers. A considerable amount of growth takes place, which, 
we are inclined to think, is so far to be attributed to the greater 
resistance that this plant offers to the exhaling influences of a 
dry atmosphere. It must be kept in mind that in many instances 
an ample supply of water in the soil does not make up for a 
greater demand on the plant, in consequence of increased evapo- 
rative force. Professor Piazzi Smyth tells us that certain trees 
do not thrive well in the dry air of TenerifFe, though they are 
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