492 
Injiuence of Climate on Cultivation. 
phere have attained their greatest heat. All plants then have 
greater powers of assimilating ammonia and carbonic acid directly 
from the atmosphere. As phosphorus and nitrogen are chemically 
associated in the vegetable structure, the abundant supply of 
the former seems to form the attraction for the latter. It is 
apparently for this reason that all annuals are benefited by a 
supply of phosphates when sown late in summer. The rapidly 
growing conditions that exist are greatly assisted by the presence 
of a fresh supply of these substances in the surface soil. It is 
easy to see that those plants which have the smallest seeds, and 
at the same time ultimately grow to the largest size individually, 
must be most benefited by phosphates. The small seed of the 
turnip, for example, does not contain as much phosphoric acid 
as will afford a supply for the formation of the rootlets which 
may run through the soil in search of other food, and, conse- 
quently, the growth of this plant is greatly assisted by dressings 
of phosphates. The beneficial effects, however, it ought to be 
borne in mind, are confined to the warm season. But even cereals 
which have comparatively large seeds are also benefited by the 
same applications when sown under similar atmospheric con- 
ditions. As might naturally be expected the sorghum or Chinese 
sugar-cane, whose seeds are small and sown during the warm 
season, has its growth amazingly increased by superphosphate of 
lime. 
Baron Liebig informs us* that the parsnip which is raised in 
the sandy soil in the village of Teltow, near Berlin, rarely weighs 
more than 1 oz. The deficiency in the physical properties of the 
soil are such that the roots are not capable of exceeding this limited 
size. This defect in the soil causes the further expenditure of 
manure to be attended with comparatively little benefit. The 
plant can only work up a limited amount of food, whether of 
ammonia or phosphate. The same variety of parsnip, however, 
grows to several pounds in weight when sown in rich soil. In 
this case, the physical properties of the soil enable the plants 
to assimilate a full quantity of food, and thus to produce large 
roots. Phosphoric manures might perhaps produce as large 
crops of parsnips on the sandy soil as nitrogenous manures 
would do, but their full development on the richer soil could 
only be obtained by the use of the latter. 
Now the same principle will serve to explain many of the 
discordant opinions that are held respecting the relative value of 
phosphoric and ammoniacal manures for the turnip crop. In the 
light and shallow soils of the chalks and gravels of England, the 
* ' Chemistry in its Application to Agriculture and Physiology,' 2nd edition, 
s. 
