ADAPTATION 129 



how the production of the mechanical tissue 

 is effected, and how the remarkable and 

 evident correspondence between its distribu- 

 tion within the plant and the various condi- 

 tions imposed by the environment is brought 

 about. 



It might seem to be a simple affair to pro- 

 duce, or at least to promote, the development 

 of mechanical tissue by merely subjecting a 

 part of the plant to an artificial stress. But 

 even if we could do this, it would still leave 

 the kernel of the matter untouched. As a 

 matter of fact, however, the attempt has 

 often been made, but the results have been 

 for the most part entirely negative. Voch- 

 ting, for example, endeavoured to induce the 

 appropriate formation of strengthening tissue 

 by attaching weights to plants in various ways, 

 and in a number of different positions. In 

 no single instance did he get a clearly positive 

 result. But what cannot be done by merely 

 applying an external force, can readily be 

 accomplished if the requisite nutritive func- 

 tions, and perhaps other internal processes 

 also, become involved. We know how the 

 growth of muscle is stimulated by use, 

 consequent, at least in part, on the better 

 nutrition which an improved condition of 

 circulation ensures. An analogous instance 

 is furnished by plants. Vochting, experi- 

 menting with certain kinds of cabbages, 

 found that after grafting heavy tops on to 

 younger and thinner stems the latter forth- 



