CHAPTER V. 



PHYSIOLOGICAL INTEGRATION IN PLANTS. 



283. A good deal has been implied on this topic in the 

 preceding chapters. Here, however, we must for a brief 

 space turn our attention immediately to it. 



Plants do not display integration in such distinct and 

 multiplied ways as do animals. But its advance may be 

 traced both directly and indirectly directly in the increas- 

 ing co-ordination of actions, and indirectly in the effect of 

 this upon the powers and habits. 



Let us group the facts under these heads : ascending in 

 both cases from the lower to the higher types, 



284. The inferior Alga, along with little unlikeness of 

 parts, show us little mutual dependence of parts. Having 

 surfaces similarly circumstanced everywhere, much physio- 

 logical division of labour cannot arise ; and therefore there 

 cannot be much physiological unity. Among the superior 

 Aly<e, however, the differentiation between the attached part 

 and the free part is accompanied by some integration. There 

 is evidently a certain transfer of materials, which is doubtless 

 facilitated by the elongated forms of the cells in the stem, 

 and probably leads to the formation of dense tissue at the 

 places of greatest strain, in a way akin to that recently ex- 

 plained in other cases. And where there is this co-ordina- 

 tion of actions, the parts are so far mutually dependent that 

 each dies if detached from the other. That though the 



