TEMPERATURE. 
85 
goes on so rapidly as to cause a vacuum in the vessels, and the 
plant droops or “ flags,” as it is called, a condition which, if not 
corrected, either by reducing the light or an extra supply of 
water, is very injurious and debilitating in its effects. For ad¬ 
vancing specimens, furnished with a powerful set of roots, the 
additional supply of aqueous food is the quickest and simplest 
mode of removing or meeting the waste occasioned by excessive 
perspiration, but with younger, unformed subjects it must be 
useless, because of their inability to take up sufficient to meet the 
demand. The remedy in the latter case consists in first reducing* 
the power of the light by the intervention of some shade, and then 
to provide against evaporation by filling the atmospheie with 
moisture, easily effected by the liberal use of watei on the paths 
or surrounding space. The most natural period for the recoveiy 
of the plants from this exhaustion is, however, at night, and that 
the reviving action may go on uninterruptedly it is essential that 
the excitability of the plant remain undisturbed, and hence tW 
necessity of a lower temperature at night a rule of the most 
vital consequence, as we may*be assured of from its occurrence 
in every region of the universe, and yet more frequently over¬ 
looked than perhaps any other law of nature. 
In the hot-houses wherein we cultivate the inhabitants of the 
tropical regions of the earth, it is of the utmost consequence that 
the rules to be deduced from these observations are closely fol¬ 
lowed, for the leading features of their native climates are so 
strongly marked as to render any deviation dangerous. Warmth 
accompanied by moisture is the principal inducement to growth ; 
warmth without moisture reduces the power of extension, so¬ 
lidifies that already formed, and induces a state of fruitfulness; 
while the absence or comparative reduction of heat removes the 
inclination to grow, or rather confines the action of the plant to 
the secretion of stores against a future active season. 
IIORTULANUS. 
