THE OUTER AND INNER TISSUES OF PLANTS. 245 



parts are subject. Given an originally-homogeneous portion 

 of protoplasm, and it follows from the general laws of Evolu- 

 tion (First Principles, §§ 149 — 155), first, that it must lose 

 its homogeneity, and, second, that the leading dissimilarities 

 must arise between the parts most-dissimilarly conditioned — 

 that is, between the outside and the inside. The exterior 

 must bear amounts and kinds of force unlike the amounts 

 and kinds which the interior bears ; and from the persistence 

 of force it follows inevitably that unlike effects must be 

 wrought on them — they must be differentiated. 



What is the limit towards which the differentiation tends ? 

 We have seen that the re-distribution of matter and motion 

 whence, under certain conditions, evolution results, can 

 never cease until equilibrium is reached — proximately a 

 moving equilibrium, and finally a complete equilibrium (First 

 Principles, §§170 — 175). Hence, the differentiation must 

 go on until it establishes such differences in the parts as 

 shall balance the differences in the forces acting on them. 

 When dealing with equilibration in general, we saw that this 

 process is what is called adaptation (First Principles, § 173) ; 

 and, in this work, we saw that by it the totality of func- 

 tions of an organism is brought into correspondence with the 

 totality of actions affecting it (§§ 159 — 163). Manifestly in 

 this case, as in all others, either death or adjustment must 

 eventually result. A force falling on one of these minute 

 aggregates of protoplasm, must expend itself in working its 

 equivalent of change. If this force is such that in expend- 

 ing itself it disturbs beyond rectification the balance of the 

 organic processes, then the aggregate is disintegrated or de- 

 composed. But if it does not overthrow that moving equi- 

 librium constituting the life of the aggregate, then the 

 aggregate continues in that modified form produced by the 

 expenditure of the force. Thus, by direct equilibration, con- 

 tinually furthered by indirect equilibration, there must arise 

 this distinction between the outer part adapted to meet outer 

 forces, and the inner part adapted to meet inner forces. And 



