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DECAYED PliAE-TKZS, 



CHAPTER X. 



PBINCIPLES OP VEGETATIO]Sr AND MODES OF" 

 PBOPAGATIOl^r. 



250. Plants are organic bodies^ composed of an outer bark or epidermis^, and: 

 an interior, consisting of an irritable elastic cellular tissue, through which 

 the sap necessary for its support rises from the root towards the upper part, 

 namely the leaves and flowers. Each cell forms a small closed vesicle, a com- 

 plete laboratory in itself, through whose membranes the sap oozes by the 

 process of osmosis ; they stand side by side filled with most different matters,, 

 which never become intermixed. Each of these cells extracts from the con- 

 stantly passing current of saj:) those constituents required for its own product,, 

 and when its allotted elaboration is completed, they are either passed on agoin 

 in a fluid state, or reserved for the future needs of some other part of the 

 plant, or they are used to repair or increase its own solidity. Plants are thus 

 possessed of a vital principle, only differing in form and intensity from that 

 oi animals. 



-251. The water-plant Chara, through which the sap may be seen circulating- 

 in a current of green globules, rising through one set of transparent cells and 

 descending through another, is usually advanced as a proof of this, and the' 

 evidence is rendered more convincing if a ligature be tied round the centre : the 

 motion continues as before, but is confined to each end, — two endless chains in 

 place of one. Dutrochet, who was at one time opposed to the theory of vital 



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