128 



LETTERS ON TREES. 



or semi-fluid matter. It really consists of cells of a 



^. , ^ very delicate texture. In 



Fig. 16. *^ 



figure 16, a transverse 

 section of it is given, in 

 connection with a plant 

 of one year's growth. 

 Immediately beyond the 

 woodv bundles already 

 formed {a a), there lies a 

 mass of cells of a semi- 

 lunar form (6 6), cut off, 

 so to speak, by a bounding 

 line from those bundles on the one hand, and from the 

 general cellular basis on the other. These cells are 

 that part of the Cambium-layer out of which the 

 woody bundles of next year will be evolved. Lying 

 directly beyond and around these semi-lunar masses 

 of cells, is the remainder of the Cambium-layer, con- 

 sisting likewise of cells. 



11. Such is the condition of the tree in Autumn, 

 and such the provision made for the growth of next 

 year's tree-plants. In spring, the bud, growing in the 

 first instance at the expense of the pith, sends out a 

 shoot, which rises upwards and puts forth leaves ; sap 

 ascends from the soil and passes to the leaves. Being 

 there elaborated, a portion of this sap again descends, 

 in order to the development of the Cambium-layer. 

 From all that portion of this layer that as yet exists 



