RUBBER PLANTING 45 



bark. The granules consist of groups of thick-walled 

 stone cells. Owing to the small size of these groups, 

 they offer little obstruction to the passage of a tapping 

 knife, but they quickly turn the edge of a razor, making 

 the preparation of microscopic sections of the bark a 

 matter of some difficulty. The granular layer passes 

 insensibly into a very soft white layer, which imme- 

 diately adjoins the wood. These four layers make up 

 the bark as popularly understood. If the bark is 

 stripped from the tree, separation takes place at the 

 cambium, which is destroyed in the process of stripping. 



Minute anatomy of Hevea bark. 



The networks of laticiferous vessels in Hevea are 

 seen in transverse section to be separated in the radial 

 direction by about five rows of cells and other elements. 

 Many of these are actually the sieve tubes and com- 

 panion cells of the phloem. No radial connections have 

 been observed between the several networks, which 

 appear to extend completely round the stem, being 

 thus concentric and having no communication with one 

 another. The arrangement of the cells composing the 

 networks is seen more clearly in longitudinal sections. 

 In the younger networks, close to the cambium, the 

 remains of the cell-walls may still be seen partly block- 

 ing the interior of the vessels; in the older vessels the 

 transverse and most of the longitudinal walls between 

 adjoining cells become absorbed. Two stages in the 



