ABSORPTION OF FOOD-SALTS BY LAND-PLANTS. 87 
line, for as a rule they describe a spiral as they elongate. Their movement seems 
as though it were for discovering the most favourable parts of the earth for absorp- 
tion and attachment. In this manner they penetrate into the interspaces in the 
earth which are filled with air and water. They also have the power of thrusting 
aside minute particles of earth, especially if the latter consists of loose sand or mud. 
If they strike perpendicularly a solid immovable bit of earth, they bend aside 
and grow round it with their surfaces closely adpressed to that of the obstacle until 
they reach the opposite point on the other side, when they once more resume their 
original direction (fig. 12°). When they encounter large grains of earth they 
Fig. 12.—Absorptive Cells on Root of Penstemon. 
1 Seedling with the long absorptive cells of its root (“‘root-hairs”) with sand attached. 2The same seedling; the sand 
removed by washing. % Root-tip with absorptive cells; x10. 4Absorptive cells with adherent particles of earth. 5Section 
through the root-tip; x60. 
sometimes stop and swell up to the shape of a club. The club divides into two or 
more arms, which grasp and cling to the granule like the fingers of a hand. Many 
fragments of earth remain thus in the grasp of finger-like processes, whilst others 
are held fast in the knots and spirals of corkscrew-shaped root-hairs which are 
often found tangled together. But the retention of most of the earth-particles 
which adhere to a plant, including fragments of lime, quartz, mica, felspar, &e., as well 
as plant-residues, is due to the fact that the outermost layer of the absorptive cells 
is sticky, it being altered into a swollen gelatinous mass which envelops the 
particles. When this sticky layer becomes dry it contracts and stiffens, and the 
eranules partially imbedded in it are thereby cemented so tightly to the absorptive 
cells that even violent shaking will not dislodge them. 
In the case of most seedlings, and in that of grasses, the absorptive cells which 
proceed from the roots and which are especially numerous in the latter, are generally 
thickly covered with particles of earth (see fig. 12*). If such a root is pulled out 
of sandy soil it appears to be completely encased in a regular cylinder of sand (fig. 
121). A root of Clusia alba, taken from coarse gravel, had its root-hairs so tightly 
