GROWTH AND SECRETIONS. 69 



stance called cambium ; in which the rudiments 

 of the cellular tissue that is to form part of the 

 new layer of wood, after a time present them- 

 selves. Even if this cambium be drawn oif from 

 the stem, its particles shew a tendency to arrange 

 themselves in a form resembling that of cells 

 and vessels ; though no perfect tissues are pro- 

 duced by this kind of coagulation."* When 

 this cambium is formed, the tree is said to be in 

 sap. The gradual solidification of the tissues 

 then proceeds, but the leaves continue to take up 

 nourishment, till, after some months of spring 

 and early summer, they are loaded with earthy 

 and carbonaceous particles, and then the buds 

 which are situated at their axils become com- 

 paratively more active than the leaves them- 

 selves, and now absorb the sap, while the leaf 

 wholly or in part ceases to do so. This effect, 

 taking place before the year is sufficiently ad- 

 vanced to check the second vegetation (or mid- 

 summer shoot, as it is called), continues, and 

 fresh branches are developed. At length the 

 leaves in autumn, being too much encumbered 

 with solid matter to retain any activity, cease to 

 perform their functions, and finally die. Then 



* Carpenter's Veg. Phys. p. 208. 



