26 DARWINISM STATED BY DARWIN HIMSELF. 



the one point in common, that their upper surfaces avoid 

 facing the zenith,- often with the additional fact that 

 they come into close contact with opposite leaves or leaf- 

 lets, clearly indicates, as it seems to us, that the object 

 gained is the protection of the upper surfaces from being 

 chilled at night by radiation. There is nothing improb- 

 able in the upper surface needing protection more than 

 the lower, as the two differ in function and structure. 

 All gardeners know that plants suffer from radiation. It 

 is this, and not cold winds, which the peasants of South- 

 ern Europe fear for their olives. Seedlings are often pro- 

 tected from radiation by a very thin covering of straw ; 

 and fruit-trees on walls by a few fir-branches, or even by 

 a fishing-net, suspended over them. There is a variety 

 of the gooseberry, the flowers of which, from being pro- 

 duced before the leaves, are not protected by them from 

 radiation, and consequently often fail to yield fruit. An 

 excellent observer has remarked that one variety of the 

 cherry has the petals of its flowers much curled back- 

 ward, and after a severe frost all the stigmas were killed ; 

 while, at the same time, in another variety with incurved 

 petals, the stigmas were not in the least injured. 



We are far from doubting that an ad- 

 ditional advantage may be thus gained ; and 

 we have observed with several plants, for instance, Des- 

 modium gyrans, that while the blade of the leaf sinks 

 vertically down at night, the petiole rises, so that the 

 blade has to move through a greater angle in order to 

 assume its vertical position than would otherwise have 

 been necessary ; but with the result that all the leaves 

 on the same plant are crowded together, as if for mutual 

 protection. 



We doubted at first whether radiation would affect in 



