ELEMENTS OF BOTANV. 



Roil, never olonp.itos by intorcfllnl'ir gvowtli, but only incrrnacs its lenpftli 

 !)}• iidditioiiH to its j^i'owiii}^ extroinity. Uh incrcuyo in tliiimoter is uccum- 

 plislied in the Hiuuo inixiintT as that of tho-Htom. 



Without onteriuf,' too ininutcly into the Htnicture of 

 tlic growing,' extremity of the root, it in neccswiry to ob- 

 Hcrvc that this is luado up of a iiianH of colls which nuil- 

 liply rapidly inul are cunstuntly building- up tissue (Fij,'. li) 

 in a forward direction. Tlmy are, nion.'over, endowed with 

 the power of rapid al:)Horptiou, and are, in faet, the innu- 

 merable moutli!^ which feed the growin<» i)lant. In order to 

 increase the absorbinjif surface of the roots, the youuf^'er 

 v)ues ar(! pi'ovided with elonpjated cells, commonly called 

 root-hairs. Thou<?h of microscoi)ic siz(!, these are pro- 

 duced in such infinite iuunl)ers as to be of immense ser- 

 vice. .As, however, they are only required durinjjj the pe- 

 riod of active <?rowth, they are not evident in autumn after the season's 

 work is accomplished. 



FifJ. M.-Th(. 

 (TTovvinti rxtri'inity 

 iif a runt, with riM)t- 

 liiiirs. MiikiiIIUhI. 



FUNCTIONS OF ROOT.S. 



Tlio mechnnical functions of the roots in supportinp^ the stem have 

 already been alluded to. We have now to consider their other imiwrtant 

 ollices. 



As animals feed upon plants, so plants feed upon minerals. And as 

 they are not pro dded with organs for the mastication of their food, they 

 nuist necessarily receive it in a strte of subdivision suited to their needs 

 and powers of absorption. In this foi'm tlujy find it in tin; damp earth 

 wliich their roots penetrate. Every rootlet is a seeker for f()r)d and every 

 <j[rowin<:j cell is hun^-ry. Water, with <,'ases and mineral salts in solution, 

 is <>reedily sucked up and carried toward the suidi;^ht for elaboration. 



Roots are, moreover, endowed, to some extent, with the power of se- 

 lecting the proper nourishment for the plant which they feed, and they 

 will take this or notliing. The most careless farmer has learned that he 

 cainiot successfully raise the same crop on a field year after j-car without 

 fertilizers. The explanation is simple. Suppose corn be planted year 

 after year in the same ground. The roots of each succeeding crop liud 

 less and less nourishment, until finally partial or complete starvation re- 

 sults. And this occurs, too, while there may be still plenty of food lit for 

 other plants. 



Hence the rotation of crops, a princii:)lo at the foundation of successful 

 farming, depends upon the selective powers of roots. 



But all plants are not fixed in the soil and do not draw their nourish- 

 ment from it. Many aquatic plants float in the Avater ; these find their 

 j)roper food iu that element. Others are parasitic upon the stems or roots 



