ROOTS AND THE SOIL. 121 



modified by differences in the soil. It is also modified 

 in accordance with the nature of its continual struggle 

 for existence underground. Within limits, the root- 

 system can be varied to suit the varying conditions of 

 soil and moisture. In loose, light, and easily-moved 

 sand, it is sometimes extraordinarily long and greatly 

 branched. Nettles in light organic soil, near human 

 dwellings, may be over seven or eight feet. The little 

 Honckenya peploides, of which some six inches only is 

 usually visible above the sea sand, may have under- 

 ground stems and roots 9-12 feet long, and if covered 

 over, it can grow upwards through a thickness of 1 2 

 indies of soil. 



On the other hand, in dense, hard-packed earth, the 

 root system is bushy and compact. The Wild Radish 

 can be forced to form a round or globular root in 

 heavy, close soil, and an elongated one in loose and 

 light earth. 



With these inherited tendencies and varied powers 

 of adaptation, it is clear that roots are well able to 

 reach the ascending films of water. The manner in 

 which they work can be easily understood from their 

 anatomical structure. 



As seen in the cross or transverse section (and 

 represented diagrammatically), the cells are arranged 

 somewhat as follows : 



First, on the outside are the absorbing root hairs, of 

 which there may be as many as 230 or even 400 on a 

 square millimetre of the surface. These can exercise 

 some force during their growth and push aside 

 particles of earth ; they can also adapt themselves to 

 the shape of the earth particles, often appearing to 

 surround or enclose them. Next comes a broad belt 

 of roundish, not specially remarkable, cells, the cortex of 



