172 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



of what has been inherited, but that at present we regard 

 morphogenesis proper as an accomplished fact. Morpho- 

 genesis proper has laid the general lines of organisation ; 

 and now adaptation during the functional life, so to speak, 

 imposes a second kind of organisation upon the first. It 

 is for that reason that the meaning of the word " cause ' 

 is now becoming a little different from what it was 

 before. 



In order to study a little more in detail what has been 

 discovered about morphological adaptation in animals and 

 plants, let us separate our materials into two groups, one 

 of them embracing adaptations with regard to functional 

 changes from without, the other adaptations to those 

 functional changes which come from the very nature of 

 functioning. Almost all of our previous general con- 

 siderations have applied to the former group, with which 

 we shall now proceed to deal. 



ADAPTATIONS TO FUNCTIONAL CHANGES FEOM WITHOUT 1 



The differences between plants grown in very dry air, 

 very moist air, and water, respectively, are most distinctly 

 seen in all the tissues that assist in what is called 

 transpiration, that is, the exchange of water-vapour between 

 the plant and the medium, but especially in the epidermis 

 and the conductive fibres, both of which are much stronger 

 in plants grown in the dry. Indeed, it seems from ex- 

 periments that transpiration is the most essential factor 

 to which " adaptation " occurs in amphibious plants, though 



1 Compare Herbst, Biol. Centralbl. 15, 1895 ; and Detto, Die Thtorie der 

 direJcten Anpassung, Jena, 1904. A full account of the literature will be 

 found in these papers. 



