78- 



COURSE OF THE SAP. 



PT. II. 



as the outer skin or cuticle of the stem is of the cuticle 

 of the leaves and buds. 

 There is All physioloo^ists talk of the circulation of the sap : 



no true L J i 



SThetip^ ^^^^ ^^^^ expression must be used, though it is a very 

 t'he^Mof incorrect one; that is, no one, I believe, has asserted, 

 nor can we suppose any one to imagine, that there is a 

 true circulation of the sap of plants, like that of the 

 blood of animals. By the circulation of the sap is 

 meant merely its ascent through the wood into the 

 leaves and buds, thence into the green outer pith of the 

 bark, on which the leaves and buds are situated, and 

 its descent to the roots, through the living parts of the 

 bark. How the descent dies off and stops, it is difficult 

 to imagine ; but it is still more difficult to suppose that 

 any part of the sap should re-ascend. The whole affair, 

 however, is a matter of the merest conjecture. 



The ' projjer juices' of plants are found in this 

 green ' herbaceous envelope ;' for example, resin in the 

 fir : and the woods of different trees do not differ more 

 in their proper constituents than the barks of different 

 trees; [ind, j^ossibly, as the first herbaceous envelope is 

 burst and destroyed, the next ring of pith assumes its 

 functions. 



Let the practical man guard these external piths 

 from external injury. Besides the gnawing of horses, 

 cattle like to find soft-barked trees, such as Scotch firs, 

 &C-, of a size that they can take between their horns to 

 rub their foreheads against, and do infinite mischief in this 

 way. Trees that are too large for this are comparatively 



