484 
Injhimce of Climate on Cultivation. 
irrigated. The temperature is as high there as in other parts of 
the torrid zone where these trees flourish, but the due amount of 
vapour in the air is wanting. Horticulturists, too, know that 
abundance of water at the roots of plants, in a hot-house, is no 
compensation for a want of the same element in the gaseous form, 
which has the effect of checking that excessive transpiration 
through the leaves, which seems to have an exhausting effect on 
the vital energies of many plants. It may be observed that 
these facts also indicate that the growth of a plant is not in 
projiortion to the amount of water that passes through its struc- 
ture, but rather the contrary. So we may naturally expect that 
many plants are fitted for particular soils and climates, by the 
resistance which their leaves offer to the exhaling influences of 
the atmosphere. In the absence, however, of direct experiments 
on the evaporative powers of different plants, our deductions are 
only put forth as mere suggestions for the explanation of facts 
that experience has made known. 
The rye plant strikingly exhibits the effects of what may be 
termed the climate of the seasons. Its greater power of econo- 
mising or husbanding the moisture of the soil appears to impart 
to it certain advantages when sown in summer, for it then groAvs 
very freely. Like most other cultivated plants, too, it shows 
comparatively little tendency to seed when sown in the hot 
season, but, on the other hand, produces a great profusion of stems 
and leaves. Such a luxuriant growtli could only be obtained in 
spring by a large expenditure of nitrogenous manures, which 
clearly shows that to a certain extent temperature acts as a com- 
pensation for manure. The common varieties and the St. John's 
Day rye, especially Avhen sown about the summer solstice, even 
in the warmer parts of the continent of Europe, become valuable 
forage-plants by producing an abundance of soft succulent stems 
and leaves. 
Flax. — A great many very curious opinions have long existed 
respecting the exhausting qualities of the flax crop. All the 
Roman agricultural writers, without exception, regarded it as one 
of the most exhausting crops that could be put into the ground. 
The same notions seem to have been entertained throughout the 
middle ages, and to have descended to our times, as the articles 
of many a lease both in Scotland and England bear witness. 
Chemical analysis does not assist us in arriving at any just or 
satisfactory conclusion on tlie subject. At least, analysis is only 
of a negative kind of aid, sliowing that this crop cannot rob the 
soil to a greater extent of its valuable constituents than others do. 
But we submit that the whole question is most satisfactorily 
cleared up by examining the facts from the same points of view 
as we have already done in the case of the cereals. Indeed, this 
