38 THE OAK. 



nearly horizontal radiating cylinders of soil are placed 

 under contribution as before. Then the secondary root- 

 lets emit tertiary rootlets in all directions these and 

 the rootlets of a higher order growing without any par- 

 ticular reference to the direction of gravitation, light, 

 etc. and so place successive cylinders of soil in all di- 

 rections under contribution as before. By this time, 

 however, the symmetry of the root-system is being dis- 

 turbed because some of the rootlets meet with stones or 

 other obstacles, others get dried up or frozen, or gnawed 

 off or otherwise injured, and the varying directions in 

 which new growths start and in which the resistances 

 are least, influence the very various shapes of the tan- 

 gled mass of roots now permeating the soil in all direc- 

 tion's. 



These roots supply the ever-increasing needs for 

 water of the shoot-system, the leaf -surface of which is 

 becoming larger and larger, and as the greater volume 

 of water from the gathering rootlets has all to enter the 

 stem via the upper part of the main root, we are not 

 surprised to find that the latter thickens, as does the 

 stem ; and so with all the older roots they no longer 

 act as absorbing roots, but become merely larger and 

 larger channels for water, and girder-like supporting 

 organs. 



