THE VEGETATIVE ORGANS OF PLANTS. 243 



abundant in poor than in good soils, and appear to be 

 most numerously produced from roots which have other 

 wise a dense and unabsorbent surface. The roots of those 

 plants which are destitute of hairs are commonly of con 

 siderable thickness and remain white and of delicate tex* 

 ture, preserving their absorbent power throughout the 

 whole time that the plant feeds from the soil, as is the case 

 with the onion. 



The Silver Fir, (Abies pectinata,} has no root-hairs, but 

 its rootlets are covered with a very delicate cuticle highly 

 favorable to absorption. The want of root-hairs is further 

 compensated by the great number of rootlets which are 

 formed, and which, perishing mostly before they become 

 superficially indurated, are continually replaced by new 

 ones during the growing season. (Schacht, Der Baum, 

 p. 165.) 



Contact of Roots with the Soil. The root-hairs, as 

 they extend into the soil, are naturally brought into close 

 contact with its particles. This contact is much more in 

 timate than has been usually supposed. If we carefully 

 lift a young wheat-plant from dry earth, we notice that 

 each rootlet is coated with an envelope of soil. This ad 

 heres with considerable tenacity, so that gentle shaking 

 fails to displace it, and if it be mostly removed by vigor 

 ous agitation or washing, the root-hairs are either found 

 to be broken, or in many places inseparably attached to 

 the particles of earth. 



Fig. 40 exhibits the appearance of a young wheat- 

 plant as lifted from the soil and pretty strongly shaken. 

 $, the seed ; #, the blade ; e, roots covered with hairs and 

 enveloped in soil. Only the growing tips of the roots, w, 

 which have not put forth hairs, come out clean of soil. 

 Fig. 41 represents the roots of a wheat-plant one month 

 older than those of the previous figure. In this instance 

 not only the root-tips are naked as before, but the older 



