482 
Injluence of Climate on Cultivation. 
other practices, wheat takes the place of rye. The history of 
Norfolk farming bears ample testimony to this revolution in the 
cropping of weak sandy soils. 
Ctiemical analysis fails to show that rye can dispense with any 
of those constituents which are found in the straw and grain of 
wheat : it rather indicates that an explanation of the requirements 
of the two plants will only be found in differences in their physi- 
ological structure. The whole of these differences we may not be 
able to trace, nor do they all come within the scope of this paper. 
It is only such as are connected with climatic agents with which we 
have to do, and which in all probability are the most influential. 
It is well known that rye flourishes on dry and sandy soils, 
where other cereals do not thrive. This fact is best accounted 
for, perhaps, by supposing that rye evaporates less water during 
its growth than wheat. One of the chief ends of marling, clay- 
ing, or vegetable manuring, is to improve the physical properties 
of soil which consist in retaining moisture for the plants that 
grow upon it. In moist climates it is found that such means of 
adding to the fertility of land are less required. For this reason, 
wheat succeeds much better after green crops on the light sands 
of the west coast of England and Ireland than it does in Norfolk. 
In the latter county, evaporation being greater, artificial means 
must be used for increasing the absorbent and retentive powers 
of the soil for moisture, in order to supply the greater demands 
of the wheat crop. The fact of rye requiring less moisture, at 
the same time that it takes up as much food as wheat from the 
soil, implies that the quantity absorbed is by no means in pro- 
portion to the amount of water that is transpired by the leaves. 
Such a principle, it appears to us, requires to be recognised in 
accounting for the suitability of different crops to different soils 
and climates. 
The scientific world is at present divided on this subject. 
Professor Way's experiments showed that the nutrient matters 
of plants are fixed by soils and rendered to some extent in- 
soluble. Some writers, however, maintain that the insolubility 
of the food of plants is not so absolute in its character as to 
prevent plants taking up in the water which evaporates through 
their leaves as much earthy matter as is found in their ashes. 
Rain-water dissolves a certain amount of earthy matters, which, 
it is considered, are sufficient to supply plants with all the food 
they derive from the soil. Experiments show that the quantity 
of water which plants evaporate is indeed great, and in some 
cases it may be amply sufhcient to convey into their structure a 
full supply of mineral matters, although these are only very 
sparingl}' soluble. On the other hand, some believe that a special 
absorbing function exists in the roots of j)lants, whereby they 
