BARK 83 



yellowish pustules or openings in the outer skin. 

 These are called lenticels and consist of very loosely 

 arranged tissue, through which air and water-vapour 

 can pass in or out. They are formed underneath 

 the stomas when, owing to the formation of cork the 

 latter are cut off, and die along with the epidermis ; 

 and to a certain extent they take their place, allow- 

 ing the carbon-dioxide respired by the living tissues 

 close by to escape. But they differ from stomas in 

 that they do not open and shut, and therefore do not 

 in any way control the amount of air and water- 

 vapour passing through. 



Later on, when the bark is more fully formed and 

 its outer layers become dry and peel off, the lenticels 

 of course are destroyed too, and there appear to be 

 then no regular passages for the interchange of air. 

 In a few trees the epidermis persists for a long time 

 and when the bark is formed it is thin and does not 

 fall away. In consequence the leaf-scars remain visible 

 even when the branch or trunk is a foot thick. 



This occurs in FICUS RELIGIOSA, the Peepul, 



ACACIA MELANOXYLON, the Black wattle, PLUMERIA 



ACUTIFOLIA, the Pagoda tree, INGA DULCE, the Koru- 

 kapuli, and others. We can see the leaf -scars on quite 

 old trunks or branches, extending,' it may be, six inches 

 or even a couple of feet in length across the surface. 

 This is because the outer layers have not died but have 

 lived and grown with the growth of the part, and so the 

 scar has extended with them. It is instructive to note 

 that while leaf-scars and bud-scars are pulled out side- 

 ways by the natural stretching of the bark as the 

 trunk or branch grows in thickness, as stated above, 



