THE OUTER TISSUES OF PLANTS. 253 



the consequences of indirect equilibration. They are not 

 due to the immediate actions of unlike incident forces on 

 the parts of the individual plant ; but they are due to the 

 actions of such unlike incident forces on the aggregate of 

 individuals, generation after generation.* 



§ 276. The unity of interpretation which we here find for 

 phenomena of such various orders, could hardly be found 

 were the phenomena otherwise caused. That the stronger 

 and the feebler contrasts among the different parts of the 

 outer tissues in plants, should so constantly occur along with 

 stronger and feebler contrasts among the incident forces, is 

 in itself weighty evidence that unlike outer actions have 

 caused unlike inner actions, and correspondingly-unlike struc- 

 tures ; either b}^ changing the functional equilibrium in the 

 individual, or by changing it in the race, or by both. 



Even in the absence of more direct proof, there would be 

 great significance in the marked differences that habitually 

 exist between the exposed and imbedded parts of plants, 

 between the stems and the leaves, and between the upper and 

 under surfaces of the leaves. The significance of these diffe- 

 rences is increased when we discover that they vary in degree 



* This seems as fit a place as any for noting the fact, that the greater part 

 of what we call beauty iu the organic world, is in some way dependent on 

 the sexual relation. It is not only so with the colours and odours of flowers. 

 It is so, too, with the brilliant plumage of birds, and with the songs of birds, 

 both of which, in Mr. Darwin's view, are due to sexual selection ; and it is 

 probable that the colours of the more conspicuous insects are in part similarly 

 determined. The remarkable circumstance is, that these characteristics, which 

 have originated by furthering the production of the best oflfspring, while they 

 are naturally those which render the organisms possessing them attractive to 

 one another, directly or indirectly, should also be those which are so generally 

 attractive to us— those without which the fields and woods would lose half 

 their chaim. It is interesting, too, to observe how the conception of human 

 beauty is in a considerable degree thus originated. And the trite obser- 

 vation that the element of beauty which grows out of the sexual relation 

 is so predominant in aesthetic products— in music, in the drama, in fiction, in 

 poetry— gains a new meaning when we see how deep down in organic natuis 

 this connexion extends. 



