92 APPLIED BIOLOGY 



water, in one case into the root by the cell-substance, and in 

 the other case into the diffusion-shell by molasses. Roots, 

 then, get the water from the soil by a process called absorption 

 or osmosis, which is due to the power of cell-substances 

 to " attract " water through the delicate walls of the root 

 cells, especially of the root-hairs. 



90. In what Part of the Root does Water ascend to the 

 Stem ? Our experiment on root-pressure ( 86) showed that 

 water passes from the soil through the root into the stem. It 

 has been stated that water gets into the root through its 

 surface, particularly through the root-hairs, which greatly 

 increase the amount of surface cells for absorption. What is 

 the path of water through the root on its way to the stem ? 

 The following experiment gives the answer. 



(D) Cut off the small end of a slender root of carrot or parsnip, 

 or any other plant large enough for convenience in cutting sections ; 

 place cut end of root in a bottle of red ink (eosin in water) ; after 

 several hours cut transversely in several places, and note the posi- 

 tion of the red-colored water in the tubes in the woody part (in 

 fibro- vascular bundles, 70). Some of the ink after a time soaks 

 out (osmoses) into the cells in the bark and pith of the root. Thus 

 water from the soil is distributed to cells by the wood-tubes. 



91. Why Water ascends Stems. There are many evi- 

 dences that water is continually ascending the stems of 

 plants to the leaves. For example, if we cut the stem off any- 

 where between the root and the leaves, the result is that 

 the leaves soon wither and dry up, while similar leaves with 

 the natural connection to the root through the stem remain 

 fresh and well supplied with water. We have already studied 

 the rise of water from the soil into the root and from the root 

 into the stem. What causes the water to ascend the stems 

 of plants? This is still one of the unsolved problems of 

 botany. Root-pressure, as we have seen ( 86), is enormous. 

 In a young birch sapling it has been found to be great enough 

 to raise a column of water 18 meters (how many feet ?) . But 



