620 DECLINE OF THE SYSTEM. 



will inevitably bring on the decline, and ulti- 

 mate destruction of the system.* The process 

 of consolidation, begun from the earliest period 

 of developement, is still advancing, and is pro- 

 ducing in the fluids greater thickness, and a 

 reduction of their total quantity ; and in the 

 solids, a diminution in the proportion of gelatin, 

 and the conversion of this element into albumen. 

 Hence all the textures acquire increasing so- 

 lidity, the cellular substance becomes firmer and 

 more condensed, and the solid structures more 

 rigid and inelastic : hence the tendons and liga- 

 mentous fibres growing less flexible, the joints 

 lose their suppleness, and the contractile power 



* It would appear from the researches of De Candolle, that 

 the vegetable system is not, like the animal, subject to the 

 destructive operation of internal causes ; for the agents which 

 destroy vegetable life are always extraneous to its economy. 

 Each individual tree is composed of an accumulation of the shoots 

 of every successive year since the commencement of its growth ; 

 and although, from the continued deposition of lignin, and the 

 consequent obliteration of many of its cells and vessels, the vi- 

 tality of the interior wood maybe destroyed, and it then becomes 

 liable to decay by the action of foreign agents, yet the exterior 

 layers of the Zi6er still vegetate with undiminished vigour; and, 

 unless injured by causes extraneous to its own system, the life of 

 the tree will continue to be sustained for an indefinite period. 

 If, on the other hand, we were to regard each separate shoot as an 

 individual organic body, and every layer as constituting a dis- 

 tinct generation of shoots, the older being covered and enclosed 

 in succession by the younger, the great longevity of a tree would, 

 on this hypothesis, indicate only the permanence of the species, 

 not the indefinitely protracted duration of the individual plant. 



