THE OUTER AND INNER TISSUES OF PLANTS. 233 



changes going on in it, lies between the bark and the mass 

 of the axis ; and is the place from which the differentiations 

 producing these proceed in opposite directions. 



But we are here chiefly concerned with the more general 

 interpretation, which is independent of any such speculation 

 as the foregoing. These contrasted tissues and the contrasted 

 functions they severally perform are, beyond question, sub- 

 ordinated to the relations of outside and inside. And the 

 evidence makes it tolerably clear that the unlike actions of 

 forces involved by the relations oi outside and inside, deter- 

 mine these contrasts partly directly and partly indirectly. 



