2 THE STORY OF PLANT LIFE 
But it is now recognised that the physical surround- 
ings play a great part in the shaping of species, apart 
from their diversity and the fact that these diversi- 
ties are correlated with plant distribution and plant 
variation. 
If, indeed, we can determine the requisite surround- 
ings of a plant we can more surely discover it. And 
as a great part of geographical botany is concerned 
with the discovery of the exact distribution of 
plants, it is highly valuable from this point of view 
alone. 
But this is not all, for we learn from the character 
of the surroundings its requirements as regards light, 
heat, moisture, altitude, soil, etc., and the manner in 
which the plant occurs, either in small communities, 
large ones or otherwise, helps us to obtain a much 
broader and more intelligent view of the vegetation of 
a district, or its physiognomy on a large scale, which 
in turn reveals to us the bases of scenery and land- 
scape. So that here the painter or the poet may 
join in the study of botany from a really vital stand- 
point. 
In general plants are most largely affected by three 
factors, though there are others which are connected 
directly or indirectly with these three main factors. 
These are climate, altitude, and soil. 
England and Wales, Scotland and Ireland, do not 
differ very markedly in climate compared with such 
differences as are expressed in the zones of climate, 
frigid, torrid, etc., into which the world may be 
