252 PHYSIOLOGY OF TREES. 



It is never so thickened in the roots, during win- 

 ter, as it is in the stem and branches ; the 

 warmth of the earth keeping it always in a state 

 of fluidity. 



If then the sap of trees be only as it is here 

 described, how can it possibly have the alleged 

 property of " organisation How can ligneous 

 fibres, tubes, cells, flowers, and fruit, be formed 

 out of a mass of homogeneous jelly, gum, or 

 resin? The perfect sap is said to be prepared by 

 the leaves, and, when elaborated, is returned again 

 into the interior of the plant, to form those new 

 accretions which take place during the summer. 

 If it were said that its elaboration is accom- 

 plished by the leaves perspiring away its aqueous 

 portion, and thereby leaving a more substantial 

 juice to be disposed as cement, to give solidity 

 to the wood, it would be a feasible representation, 

 and moreover, a representation that could not 

 be disproved. But when it is maintained, that 

 this elaborated juice is transformable into all the 

 other essentials of the plant, practical knowledge 

 hesitates to give its consent; because there are 



