108 
INFLUENCE OF CLIMATE ON PLANTS. 
Plants, it is well known, have a temperature altogether peculiar to themselves. 
This does not arise so much from the elicitation of latent heat — although, probably, 
internal chemical combinations may tend to increase it — but is acquired chiefly 
by the admission of warmer fluids from the soil into the roots, and their trans- 
fusion throughout the entire plant by the vessels. The power of retaining this 
temperature depends entirely on the stage of the plant's progress, and the 
consequent density or porosity of its cuticle. Unless duly preserved by a perfect 
epidermis, the extent of radiation wdll be equal to the difference between the 
temperature of the plant and that of the atmosphere. This will at once account 
for the effects of cold on the imperfectly developed or incompletely matured 
substance of plants. 
A knowledge of the laws and process of radiation, is of the greatest value to the 
cultivator of exotic plants ; as the safety of all the objects beneath his care is almost 
wholly dependent on the manner in which the reduction of temperature is pre- 
vented. Protection of all kinds may be said to consist in the effectuation of 
this simple object ; and so far only as it is conducted with that specific end in 
view, can it be either suitable or successful. 
Radiation, as we have shown, is transacted from the surface of plants, and 
caused by contact with, or exposure to, a colder atmosphere. If, then, we envelop 
tender plants in an atmosphere of their own, or obviate the transit of heat to the 
external air, by interposing some material of slow radiating power, we effectually 
preserve them from injury by frost. "When cold is not very intense, but vegetation 
extremely susceptive, as, for instance, in the spring and autumnal seasons, at which 
times the frosts are trifling, and the substance of plants only newly developed, 
or but partially organized, more especially in the latter case, a covering of any 
slight material will be sufilcient to restrain radiation from proceeding too rapidly, 
or to too great an extent. The screen, however, must always be perfectly detached 
from the plant which it surrounds, otherwise conduction will be substituted for 
radiation ; a consequence by which the remedy will be nearly nullified. 
Attempts to naturalize any exotic plants, can only issue in the desired result 
when active attention is bestowed upon the particular just named. The most 
careful preservation during the winter will be of little avail, unless a similar 
protection is nightly afforded in the decline of autumn, and the commencement of 
spring ; at least, when the atmosphere is clear, or there is any indication of 
frost. It would be difficult to decide at which of these seasons defence is most 
requisite. Although a slight consideration would lead us to declare that the 
greatest necessity existed in the spring months, because vegetation is then in a 
highly excited and impressionable condition, further investigation establishes an 
equal need for it in the fall of the year. 
In the autumn, both the soil, and the plants growing on it, are more highly 
imbued with heat than the atmosphere ; and hence, the excessive radiation which 
takes place during the cool night hours of that season isj on account of its 
