38 THE OAK 



grows out at an obtuse angle from the primary root, 

 and not vertically downwards, and as it does so a 

 similar wave of root-hairs is developed along it ; thus a 

 series of nearly horizontal radiating cylinders of soil 

 are placed under contribution as before. Then the 

 secondary rootlets emit tertiary rootlets in all direc- 

 tions these and the rootlets of a higher order growing 

 without any particular reference to the direction of 

 gravitation, light, &c. and so place successive cylin- 

 ders of soil in all directions under contribution as 

 before. By this time, however, the symmetry of the 

 root-system is being disturbed 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 tangled mass of roots now per- 

 meating the soil in all directions. 



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 absorb- 

 ing roots, but become merely larger and larger channels 

 for water, and girder-like supporting organs. 



