Absorbing Surfaces of Roots 55 



and water and coal, stations itself in any fertile soil, and does its 

 work with the warmth of a summer day. 



In all our problems of land drainage and irrigation, we are 

 searching to better understand, and through this better under- 

 standing to better meet, the conditions under which a system of 

 roots can best do. its work. But the foundation of such an under- 

 standing should be a knowledge of the root itself, and how it 

 places itself in the soil in order that it may do its work. Let us 

 attempt, then, to present in a brief form what has been learned 

 regarding the essential features of root structure and root action. 



Roots have three distinct functions to perform in land plants 

 having green leaves : first, to absorb moisture and the salts held 

 in solution ; second, to convey and deliver into the 

 stem of the plant the water which has been absorbed : 

 and third, to act as a support to the plant and hold 

 it upright in the air and sunshine, whenever it is 

 not trailing or climbing in habit, or is without 

 stems. 



It appears to be the general conviction among 

 plant physiologists that only the very tip ends of 

 the roots are particularly serviceable as absorbing 

 agents, and that even these are serviceable for a 

 short time only. Farther than this, it is the root- 

 hairs which branch out in great numbers from them, 

 rather than the fine roots, which are the real ab- Q . 



sorbing surfaces. These root-hairs are extremely . , . 



IT .LI 11 i i 11 ji Flg.7. Root-hairs 



delicate, thin-walled tubes, usually not more than ot - mustard 



one -eighth of an inch long and a hundredth of an plants, A with 

 inch or less in diameter, which stand out on the g* 1 ^^ soli^e- 

 root surfaces like the pile on velvet. These absorb- moved. (After 

 ing root-hairs never form at the very tip end of a Sachs -) 

 new advancing root, and as, according to Sachs, they "die off 

 after a few days, they form a brush-like covering on the root 

 for a distance of half an inch to two or three inches, dying 

 off behind and forming anew as the advance is made into new 

 soil. In Fig. 7 are shown the roots of two seedling white mus- 

 tard plants, A with the particles of soil still adhering to the 



