VEGETATIVE OBGANS OF PLANTS. 



269 



plant as lifted from the soil and pretty strongly shaken. 

 S, the seed ; b, 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 parts of the primary roots, e, and of the 

 secondary roots, n, no longer retain the particles of soil ; 

 the hairs upon them being, in fact, dead and decom- 

 posed. The newer parts of the root alone are clothed 

 with active hairs, and to these the soil is firmly attached 

 as before. The next illustration, Fig. 42, exhibits the 

 appearance of root-hairs with ad- 

 hering particles of earth, when mag- 

 nified 800 diameters : A, root-hairs 

 of wheat-seedling, like Fig. 40; B, 

 of oat-plant, both from loamy soil. 

 Here is plainly seen the intimate 

 attachment of the soil and root- 

 hairs. The latter, in forcing their 

 way against considerable pressure, 

 often expand around, and partially 

 envelop, the particles of earth. 

 (Sachs's Exp. Phys. d. Pflanzen.) 

 Imbibition of water by the root. 

 The force with which active roots 

 imbibe the water of the soil is 

 sufficient to force the liquid upward 

 into the stem and to exert a continu- 

 al pressure on all parts of the plant. 

 When the stem of a plant in vigor- 

 ous growth is cut off near the root, 

 and a pressure-gauge is attached to 

 it, as in Fig. 43, we have the means of observing and 

 measuring the force with which the roots absorb water. 



Fig. 43. 



