140 TRANSACTIONS OF THE ILLINOIS 



iron, which can be replaced as fast as worn away. Each root tip is 

 furnished with a protecting, self-renewing structure as serviceable 

 as the special point of a stony-ground plow. The young, tender 

 cells are not pushed and crushed against the earth. The extreme 

 point of every root is a unique cap which, like the bark of a tree, 

 grows upon the inside and wears its oldest and hardest cells outside. 

 New layers of cells are constantly forming at the extremity of the 

 root proper, and upon the inner surface of the protecting cap, while 

 as the root advances the outer and older cells of the root-cap dissolve 

 into a slimy substance, which lubricates the hard, penetrating point 

 and assists in the boring process, by which advance is possible. It 

 is hard to find a more wonderfully contrived, or more marvellously 

 adapted organ in plants or animals than this inconspicuous but im- 

 portant little tip of a growing root. 



The surface of the elongation end of young roots is perfectly 

 smooth. The length of this part may be said to be in usual cases 

 from one-fourth of an inch to one inch. But the rest of the sur- 

 face is peculiarly clothed with long, weak, white hairs. When we 

 pull young roots from the soil these are broken off so that they are 

 not usually seen. But when plants are turned out of flower pots 

 with the ball of earth and the moss or roots undisturbed, these root 

 hairs can be easily, often conspicuously, seen. An easy and instruc- 

 tive experiment may be made b}^ putting a little damp packing moss 

 or sawdust in a wide-mouthed bottle or other glass vessel, and plac- 

 ing near the top, next the glass, some grains of corn or beans, to 

 germinate. The growing roots can be easily watched and the root 

 hairs readily seen. 



If these slender hairs grew upon the elongating portion they 

 would be inevitably torn and rubbed off against the earth; but 

 when the outstretching of the root ceases; they shoot out at right 

 angles to the axis of the root, penetrate the soil on every side and 

 become, as we shall see, the efficient agents of absorption. The 

 hairs gain the closest possible contact with the particles of the soil, 

 and to make the investment of the soil particles still closer, the 

 outer surface of the hair becomes gelatinized, in which plastic state 

 the actual and absolute contact of the hairs and the irregular sur- 

 faces of the soil elements is secured. The gelatinous material hard- 

 ens and the structure is ready for its official work. As may be im- 

 agined, the hairs are not permanent structures. They live but a few 

 months at best, and cover only young roots. As soon as bark forms 

 on the root the hairs are forever lost to that portion of the struc- 

 ture. Thus young roots are active roots. These, and these only, to 

 any considerable extent, act as absorbers for the soil. 



Extent of Boots. — Roots are commonly buried in the soil out of 

 sight, and when we dig trees and plants little study is usually made 

 of the actual depth and distance to which the small roots extend. 

 The fact is, this is usually far greater than commonly supposed. The 



