i 5 2 THE MECHANISM OF ABSORPTION AND TRANSLOCATION' 



dye is rapidly absorbed 1 . 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- 

 dolleVthat 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 falsl^ 

 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 Triticum 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. 



" 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., 1891, p. 132. 



