Sunshine, Rain, and Wind 
leaf is to combine the greatest possible capacity for work 
with the smallest expenditure of material and energy. 
And also the shape of every leaf and its internal anatomy 
in every sort of plant, are in harmony with the external 
conditions to which it is exposed, such as degree of 
moisture, chemical and physical nature of the soil and 
climate generally.® 
It is this harmony between the live plant and the 
outside world that is always a fascinating object of 
research. It can be studied in all sorts of ways. 
Sometimes the results have been most remarkable. 
There is, for instance, a little group of plants, the 
Podostemacez, which grow generally on rocks in the 
spray of waterfalls. They are all very curious, and 
some of them are so exactly like mosses or algze, which 
might occur in such places that no one except a botanist 
would ever distinguish them to be flowering plants. 
This is the case, for instance, with the little Ligea 
Glaziovii described by Warming.? 
At present most work is being done by statistical 
methods. Thousands of leaves, or of some other 
measurable unit, are examined and catalogued. Then 
those of the various localities are contrasted, and if 
possible the result of some special character, say sun- 
shine or shade, is deduced from the whole series of 
measurements. Unfortunately such calculations have 
often been carried out for many thousands of flowers and 
leaves without considering the environment at all! In 
such cases, one can see that the results simply illustrate 
not the. variation in the flower or leaf, but rather the 
different conditions or environments under which they 
have been grown! 
There is always a slight variation even amongst plants 
growing in one particular locality, even although they. 
inherit, not only the characters of their parents, but also 
183 ; 
