152 THE MECHANISM OF ABSORPTION AND TKANSLOCATION 



dye is rapidly absorbed '. By similar experiments, as well as by the lessened 

 rapidity with which plasmolysis is produced, it may be seen that in Confervae, 



rhizoids of mosses, &c., as a general 

 rule the permeability of the cell-wall 

 decreases as it grows older. The 

 supposition, originally put forward by 

 Grew, and supported by de Can- 

 dolle 2 , that the root-cap acted like a 

 sponge and absorbed the major part 

 of the water and salts which the plant 

 requires, is incorrect, and its falsity 

 has been experimentally proved by 

 Ohlert \ 



Specific types of root-system 

 are presented by different plants. 

 Thus many plants have a poorly 

 developed root-system, which soon 

 ceases to grow, while other plants 

 continue to acquire new territory 

 for a long period of time, and 

 ultimately produce very large root- 

 systems. In other plants again, 

 such as the Clover or the red Fir, the 

 tap-root buries itself very deeply 

 and hence absorbs nutriment from 

 the deeper layers of the soil, into 

 which plants with more horizontal 

 root-systems do not penetrate. 

 The latter, however, in the Pine 

 and the Poplar, cover a large surface 

 area, as is immediately obvious 

 when the roots of the Poplar ap- 

 pear projecting above the surface 

 of the ground. 



Very often, it is true, plants 

 are forced to accommodate their 

 root-systems to the conditions exist- 

 ing in the soil, and hence no con- 

 stant relation exists between the sub-aerial and the underground organs of 



FIG. 13. Seedlings of Triticitm vulgare grown in 

 garden humus. After shaking, the earth adheres only to 

 the portions bearing root-hairs, e' '. At e no root-hairs are 

 present and the lateral roots have in part died away. 

 (After Sachs.) 



1 Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. II, p. 201. 



3 De Candolle, Organographie veget., 1827, T. I, p. 260. [Hence the old term ' spongioles.'] 

 3 Ohlert, Linnaea, 1837, Bd. XI, p. 621. On roots without a root-cap, see Waage, Ber. d. Bot. 

 Ges., 1 891, p. 132. 



