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. 8 



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 

 Podostemaceae, 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 algae, 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. 9 



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 



