Relation of Climate to Vegetation. 107 
THE RELATION OF CLIMATE TO VEGETATION.’ 
By D. P. PENHALLOW. 
In conformity with the laws of Natural Selection, as 
stated by Darwin and accepted by modern biologists, condi- 
tions of environment are the determining factors in the 
growth, character and distribution of organic life. These 
conditions are nowhere uniform, and present numberless 
gradations and complications, in consequence of which 
organic life possesses characteristics which are everywhere 
subject to more or less striking variations; and if we are to 
form a correct estimate of the relations between cause and 
effect, it is essential that we first inquire into the specific 
influence upon functional activity of each one of the ele- 
ments which, in the aggregate, constitute the environment 
of any individual or species. 
Among these conditions we may note those of food supply 
and nutrition ; varying intensity and quality of light; mois- 
ture; pressure; electricity ; the presence or absence of 
certain gases and temperature ; and in this latter element 
is found one of the most important of all the factors which 
determine the normal life of a plant. We are well aware 
that certain plants are found growing in hot springs ata 
temperature of 199.4° F. or within 12.6° of the boiling point 
of water, thus representing in modern times, although in 
exaggerated form, conditions under which, in the later Laur- 
entian age ; primitive vegetation very generally flourished. 
Other plants—the red snow—are found to complete their ex- 
istence at a temperature so near the freezing point of water 
that the difference cannot be measured. But in each case 
the plant is equally sensitive to extremes of an opposite 
nature and would perish miserably were the temperature to 
be sensibly lowered in the one case or raised in the other. 
Between these two extremes, the majority of plants flourish 
at a much more moderate temperature, nevertheless, it is a 
well defined law of nature that each species thrives best at 
‘Abstract of a lecture delivered in the Somerville Course, at 
Montreal, March Ist, 1888. 
