30 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



supply of oxygen is too small, their life must cease, 

 since they need oxygen for respiration just as do other 

 living cells; if they are deprived of water, they cannot 

 grow and if they cease to grow they cannot divide, 

 and any shortcomings in the matter of water-supply 

 will have for effect a diminution of activity on the part 

 of the cambium. The same is true of the supply of 

 food-substances ; certain mineral salts brought up 

 from the soil through the roots, and certain organic 

 substances (especially proteids and carbo-hydrates) 

 prepared in the leaves, are as necessary to the life of a 

 cambium-cell as they are to the life of other cells in the 

 plant. Now, since the manufacture of these organic 

 substances depends on the exposure of the green leaves 

 to the light, in an atmosphere containing small 

 quantities of carbon-dioxide, and since the quantities 

 manufactured are in direct relation to the area of the 

 leaf-surface the size and numbers of the leaves it is 

 obvious that the proper nourishment of the cambium 

 is directly dependent on the development of the crown 

 of foliage in a tree. Again, since the amount of water 

 (and mineral salts dissolved in it) will vary with the 

 larger or smaller area of the rootlets and absorbing 

 root-hairs (other things equal), this also becomes a 

 factor directly affecting our problem. Of the inter- 

 dependencies of other kinds between these various 



