46 



TNTROBUCTORY. 



long bast cells, arranged imrallel with the axis of growth. I 

 represents the place of the cambium or growing layer of organ- 

 izable material which descends from the leaves between the 

 liber and the sap-wood during the period of groAvth. K is 



Fig. 8. 



6 H i 



woody tibre, which gives strength to the stem, and through 

 which the crude sap rises. L indicates the vessels or ducts, 

 with various markings, such as dots, rings, and spirals, which 

 are formed most abundantly in the Spring, and usually con- 

 tain no tiiiid. They convey gases and aqueous vapors, and it 

 may lie that a large pro])()iti(in ol' all tlic water ascending frtun 

 the roots to tlie leaves passes through them as a vapor. M is 

 the layer of spiral vessels or ducts which always inclose the 

 pith, and in the young shoot extend into the leaves and unite 

 them to the pith during its life, which eeases with the first 

 season. 



" This ]iart of the plant develops an annual layer of wood 

 and bark, with ravs of cellular tissue like the stem. The num- 



