84 
TEMPERATURE. 
It may be frequently observed that individuals of precisely the 
same kinds will, under certain circumstances, bear a much greater 
reduction of temperature than others differently situated; so also 
the same plant sometimes may be exposed without prejudice to 
influences that at another period would probably kill it; this 
arises from the difference in quantity and fluidity of the secretions ; 
when these are present in abundance and of an aqueous character, 
the effects of frost or cold are then more severe, and hence the 
reason of young shoots being killed sooner than old ones, and 
the greater probability of plants in a low damp situation suffering 
to a further extent than others of the same kinds on a hilly and 
exposed position. 
In cultivating a general collection of plants, it is necessary that 
the operator possess a knowledge of the character of the countries 
from whence his charge is derived, for unless the leading features 
of each are preserved in the management, but little success can 
result or the work is conducted on merely empirical rules; he 
should know not only the mean temperature of each district, but 
something of its fluctuations, and the variations in liygrometric 
pressure which characterize its seasons, together with their 
periods and duration, and then means must be provided for as 
close an assimilation as may be effected in the subsequent 
management, to the native positions of each class of the plants 
to be grown. 
The functions of vegetable life in its progress to maturity are 
carried on by two processes, the inhalation or absorption of food 
by the roots in the form of fluid, and by the leaves as gases, and 
the respiration of such of the latter as are not required in the 
assimilation of both, which takes place in the system of the plant; 
the former is most rapidly performed at night, when, by a beauti¬ 
ful provision of Nature, it is most abundant, and the latter function 
is exerted only in the day, as the presence of light is necessary 
to the elaboration of the aliment taken up by the organs of the 
plant; the rise of temperature in the day stimulates to an active 
condition, and after due secretion the superfluous watery matter 
is withdrawn by the action of the light; at night the temperature 
returns to its minimum, when the roots impel fresh matter to the 
exhausted vessels, and the plant regains its vigour. 
When the temperature of the day is excessive, the evaporation 
