Sunshine, Rain, and Wind 



vicar will represent the dominant or master species 

 found in all the best places.) But many cases are 

 known in which one can change one sub-species into 

 another, simply by transferring it to the other's territory. 



Dr. Krasan found that Potentilla arenaria became P. 

 viridis when planted on the sunny slopes where that 

 species lived. The reverse experiment with P. viridis 

 led to distinct changes in the direction of P. arenaria, 

 but not to a complete transformation.^^ 



In Servia also three at least of the high alpine plants 

 became common lowlanders when sown in the low- 

 lands."^^ ^^ Soldanella alpina replaces S. montana in the 

 higher alpine region, and many other cases might be 

 quoted.^^ 



The differences brought about by strong wind and 

 a dry or sunny atmosphere are very marked indeed. 

 Under such conditions the transpiration of water 

 becomes extreme, and the skin or epidermis cells are 

 especially affected. Their outer walls are reinforced 

 by the deposit of more and more cellulose (probably 

 due to the sacrifice of more protoplasmic elements for 

 this purpose). This change is very well shown by our 

 common bracken, which varies greatly according to the 

 place in which it grows. In shade the leaves are thin 

 and delicate, but in a dry exposed place they become 

 thick and develop a special layer of thick walled cells 

 (hypoderm). Indeed, by altering the outside conditions, 

 one can leave half a leaf to become of the dry or sun 

 type, and change the other half into the shade form by 

 arranging some sort of shelter for it.^® 



There is a very interesting account of the ^'patanas " or 

 upland district of Ceylon by Messrs. Parkin and Pearson.^' 



* Trifolium orbelicum, Aster alpinus, and Alyssum repens became T. repens, 

 A. amellus, and A. montanum. See also the interesting division of the 

 Geraniums according to climate and geography by Knuth.^° 



185 



