INFLUENCE OF CLIMATE ON PLANTS.* 
SOLAR HEAT. 
— ^ — 
Climatic differences of temperature, independently of exercising a most 
important influence on the geographical assignation of plants, essentially affect 
the various phenomena of their functions, as is illustrated and exhibited in their 
growth and products. That heat is indispensable to the excitation of vegetable 
life, is sufficiently attested by the fact that those members of plants which remain 
exposed to the chilling atmosphere, are invariably torpid during the winter season; 
and although fluids are absorbed from the earth throughout even the severest 
winters, it is only by those roots which are far enough removed from the surface 
to enjoy the degree of temperature necessary for rarefaction, and they can circulate 
only through those parts which are duly preserved from radiation by the bark. 
Vitality itself — that mysterious principle — though apparently an inherent 
property of vegetation, is dependent on heat for its continued existence. The 
power of, and proneness to procreation, may likewise be supposed to increase in 
the same ratio as the temperature ; for, in those countries where the highest 
temperature prevails, plants are met w 7 ith in greatest abundance; while, in 
proportion as the degree of latitude increases, vegetation is propagated much less 
profusely, and, as far as the researches of man can determine, disappears entirely 
on approaching the poles. 
Changes of temperature affect the substance and functions of plants in various 
ways ; but in none is their influence so conspicuous as in the expansion, extension, 
and dissolution of their structure. Development and decomposition are alike the 
consequences of heat, and vary in their progress and extent in precise accordance with 
the existing degree of temperature. It is the former of these that we propose now 
to explain. A moderate temperature will cause a gradual elongation and enlarge- 
ment of all living vegetable substances, by inducing the imbibition and circulation 
of nutritive fluids. By a considerable elevation of this temperature for any length 
of time, results of a directly contrary nature are experienced, and a perceptible 
contraction occurs. This is caused by excessive evaporation ; which expends too 
prodigally the vital juices, impoverishes the plant, and thus collapses its tissue. 
Heat incites the functions of all kinds of plants in the same manner, though by 
no means in an equal degree. The axiom that " habit is second nature," applies 
not more truly and appropriately to man than to vegetation. By long-continued 
habit, the faculties of all plants are so conformed and adapted to their native 
climate, that removal to countries of a much higher or lower temperature is always 
highly detrimental, and frequently fatal. It is possible, however, to effect a change 
in their habits, and nothing but perseverance in a judicious course of treatment is 
required to compass this end. Where the change is from a colder to a warmer 
climate, this is especially practicable. 
* Continued from page 63. 
