THE VEGETATIVE ORGANS OF PLANTS. 2485 
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, (Addes pectinata,) has no root-hairs, but 
its rootlets are covered with a very deiicate 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 1s 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, 
S, the seed; 6, 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 
