300 ACTION AND REPOSE 



which merely serves to protect the other parts from 

 external interruption or injury. [By-the-way, the 

 possession of a protecting epidermis is one of the 

 best popular means of distinction between organic 

 and inorganic beings, in those obscure species in 

 which they resemble each other the most.] 



At the close of the season, the whole of the cam- 

 bium, or changeable pulpy matter, is formed into 

 wood and bark, which adhere firmly to each other 

 at the line of separation ; and when that is accom- 

 plished, the leaves are of no further use, and they 

 change colour and fall off; for though there are ves- 

 sels apparently of a woody texture in the leaves, 

 they are not the product of the same action as the 

 wood of the tree. That action extends only to the 

 base of the petiole, or foot-stalk of the leaf, and as a 

 pellicle of epidermis gradually forms upon that, as it 

 becomes complete, the leaf separates without a 

 wound. Whenever indeed the action of a tree 

 ceases, whether naturally at the season when it 

 passes into repose, or in consequence of an external 

 check, such as transplanting it while in leaf, the last 

 action of the tree the effort of nature by which it 

 preserves its vitality is the formation of that epi- 

 dermis between the twigs and the petioles of the 

 leaves. If the tree succeeds completely in forming 

 that, and the withered leaves fall off spontaneously, 

 or can be removed by a touch, the tree may be con- 

 sidered as safe, though it may remain a long time 

 before positive action again begins ; but if the with- 

 ered leaves remain firmly on the twigs, it is a sign 

 that the tree is affected in its general action, and 

 that it will " die down" in those parts to which the 

 withered leaves adhere, if it does not perish alto- 

 gether. 



When the action of the leaves ceases, that of the 

 absorbing rootlets ceases also, because the matter 

 which is taken in by them is not convertible into 

 wood or bark without the co-operation of the leaves ; 



