62 
INFLUENCE OF CLIMATE ON PLANTS. 
On the germination of the seeds of exotic plants at a favourable season, we 
are inclined to believe that much of their subsequent capacity for naturalization 
depends. If stimulated in the latter part of the autumn, or during the winter, 
they acquire a great degree of weakness and sickliness, and what is still worse, an 
unnatural habit of commencing their growth at an unsuitable period. This will 
be in some measure retained for a considerable time ; and will inevitably retard, 
if not (by exposing their young shoots to early spring frosts) wholly subvert, all 
attempts to acclimatize them. On the contrary, by judiciously selecting that 
month for inducing their vegetation, at which they should afterwards commence 
their annual development, it appears most probable that they will immediately, 
and without thereby suffering any debilitation, accommodate the exertion of their 
functions to the vicissitudes of our climate. 
With those countries which are situated in low latitudes, it is more important 
that the lowest degree of temperature which they ever experience should be ascer- 
tained ; while, in proportion as they recede from the equator, a knowledge of 
both extremes is equally essential. Throughout the temperate zones, and as far 
as vegetation extends towards the polar circles, but more especially in those 
portions of the former which are considerably elevated, and where powerful but 
transient summer heat prevails, it is advantageous to know the highest rate of 
temperature that exists as well as the lowest ; for in many Alpine districts it is 
occasionally found to exceed the usual heat of the valleys of the same latitude. 
In such cases, vegetation having only a certain interval wherein to perfect its 
growth, progresses with amazing rapidity ; and plants spring up, mature and 
scatter their seeds, and decay, in an astonishingly brief space of time. 
Climates of very variable temperature naturally produce plants to which an 
intense degree, whether of heat or cold, is either not injurious, or decidedly bene- 
ficial. Annuals are peculiarly adapted to countries of this description, as they 
perform the necessary offices for the propagation of their species in a summer, and 
the oleaginous matters with which their seeds abound, together with the hard inte- 
gument or rind in which they are enveloped, enable them successfully to withstand 
the most severe frosts. These, and such deciduous trees as are well coated with 
bark, or evergreens in the wood of which resinous or oily juices abound, the buds 
of both being protected in a very similar manner to the seeds of annuals, or by 
tough, viscid sheaths, form the principal features in the vegetation of those divi- 
sions of the earth which are subjected to great alternations of heat and cold. Her- 
baceous plants are also abundant, but they assume a very different habit to those 
of tropical countries ; as their stems and leaves annually decay, and those of the 
succeeding year are duly protected in embryos of a form and nature precisely 
analogous to those of trees and shrubs. 
But the best and safest data whereon to found a proper estimate of the influ- 
ence of temperature on botanical geography, and especially to establish a code of 
cultivation for any particular species of plants, are accurate observations with 
