THE PHILOSOPHY AND USES OF BOTTOM-HEAT. 
157 
A principle nearly akin to this was recognised in our last Number, where the 
effect of soils was in qviestion. It is here more prominently stated, in order to 
consider the influence of another and very different agent ; for whatever good may 
accrue from the judicious selection and mixture of soils, the advantage will be little 
better than nugatory, as regards stove-plants, if they are left to become cold, and 
therefore liable, even with the best mechanical appliances, to get sour or saturated. 
In the earlier times of plant cultivation, scarcely any stove species was grown 
without being plunged in fermenting bark, or other source of bottom-heat ; and 
though the appearance of such plants certainly will not endure comparison with 
modern specimens, that are reared without such a stimulus, the latter fall almost 
equally behind those which, besides every other known advantage, are yet subjected 
to a heating power from beneath. It is thus proved that it was not the use of 
bottom-heat, but the absence of various additional expedients now in vogue, which 
kept the plants of olden cultivators in an inferior condition ; and hence, that it is 
not wise to discard a thing which the most trivial experiment will show to be of 
the utmost benefit. 
As we have asserted the importance of having healthy roots to plants, we shall 
now endeavour to indicate how the application of bottom-heat is likely to bring 
about that desirable object. That plants cannot thrive much without good roots 
may be seen by cramping them in very small pots, when the stunted specimens, so 
common in China, will be obtained. But if those very specimens, even after they 
have been so treated, were to be planted in a free congenial soil, and have every 
other necessary assistance, they would soon develop themselves in a more natural 
and healthy manner, because the roots would then have proper play, and receive 
all due stimulus. 
Now, it is well known that certain conditions of temperature, light, and 
moisture, are essential to the growth of all vegetables ; but it is sometimes for- 
gotten that a particular degree of these are quite as requisite to the roots as to the 
more exposed portions. To speak only of heat at present, a plant brought from 
the tropics may be excited by the application of atmospheric heat and moisture ; 
but its developments will never be so fine and so luxuriant as they would be if it 
had, at the same time, the aid of a stimulus to its roots from below. Growing- 
branches and foliage may serve, for a while, to impel the roots to push forth. 
They will not, however, long maintain their action, on account of themselves 
becoming weak and languid when unsupported by the roots ; and unless the latter 
begin and remain to be the first in motion, or at least advance concurrently with 
the more exposed parts, true healthiness or productiveness (that is, the highest 
degree of both) can never be realized. 
To attain the condition last mentioned, it is requisite that the heat (which is 
the principal stimulant) be as great, or nearly as great, in the pot as it is in the 
air. Where no artificial temperature is employed from below, it need not be said 
that the soil in pots, in ordinary cases, must be far colder than the atmosphere ; 
