Relation of Climate to Vegetation. 109 
temperate region—may be of so unusual and extreme a 
nature as to absolutely limit its existence. On the other 
hand, it is equally true that if the same conditions are ap- 
plied with less energy for a given time, and thus the sum 
total of the modifying influences is extended over a much 
greater period, the organism not only becomes gradually 
adapted to its new conditions of life, but under their in- 
fluence may even become permanently modified in one or 
more essential characteristics. This is a matter of common 
observation with those who are familiar with plant life, and 
such variations may be accomplished so rapidly as to be 
recognisable within the lifetime of a given observer. Thus 
it is well known that plants grown in botanic gardens, be- 
come so modified by their unusual conditions of life, that 
they no longer answer in a strictly scientific sense, to the 
description of the species in the original wild state. Similar 
variations are to be noted among wild plants as their sur- 
roundings vary. The same species growing under different 
conditions of moisture, as in wet and dry places, will present 
important differences in size, color and form ; or growing 
at different elevations, and thus under somewhat widely 
different conditions of temperature and pressure, its general 
aspect becomes wholly changed. 
It is thus not difficult for us to appreciate the fact that 
since climate involves many of the factors already enumer- 
ated, and especially temperature, it as a whole, must exert 
a preponderating influence upon plant life, not only to de- 
termine its character in a given locality, but also the range 
of distribution for various species. With these general 
principles in mind, we are prepared to examine and under- 
stand some of the relations known to exist between climate 
and vegetation, which constitutes the subject of our lecture 
this evening. 
Of the various important problems with which modern 
botanical science has to deal, that which is concerned in de- 
termining the relations between climate and vegetation is 
perhaps one of the most intricate and far-reaching. 
Climatic conditions mean, primarily, temperature and 
