THE MOLECULAR FORCES IN PLANTS. 237 



the conduction of water in the stem is thereby greatly prejudiced. 

 These various injurious results do not appear when the shoot is 

 cut through under water, as it is easy to see. 1 



1 See H. de Vries in Arbeiten d. botan. Ingtiiuts in Wiirzburg, Bd. 1, p. 287, 

 and F. v. HOhnel in Haberlandt's Wi**eiuch.~prakt. Forschungen auf d. Geliete 

 d. Pflanzenlaues, Bd. 2, p. 120. 



VII. THE ABSORPTION OF MINERAL SUBSTANCES 

 BY PLANTS. 



88. The Roots of Plants as Organs for the Absorption 

 of Mineral Substances. 



The roots serve to fax. the plant in the soil, but they also 

 function as organs for the absorption of water and mineral 

 substances. If we cultivate plants by the water-culture method 

 in aqueous food solutions, the latter function is exhibited in the 

 clearest manner. But even in the soil in which plants grow, food 

 solutions are present in abundance, for the fluids retained by the 

 elements of the soul, and circulating between them, are not pure 

 water, but dilute food solutions. Water acts upon the elements 

 of the soil, dissolving and disintegrating them. They give up to 

 the water mineral substances, absorbed or still more closely held 

 by them, and the solvent power of the water is frequently greatly 

 increased by the presence of large quantities of Carbon dioxide 

 originating in the soil through processes of decay. 



I shall not here enter into details concerning the absorption 

 of mineral substances from food solutions by roots, since this 

 question is to be considered in 89. We shall, however, refer to a 

 few observations which are of interest in connection with the 

 behaviour of roots in the soil. 



We germinate a few wheat-grains in good garden soil, in a 

 flower-pot, and carefully remove the young plants from it when 

 they have developed four or five roots. If we vigorously shake 

 the seedlings, a large part of the soil adhering to the roots falls 

 off, but a certain proportion does not loosen itself. The whole 

 surface of the roots is clothed by a layer of soil ; only the root- 

 tips are free from clinging particles of soil. Careful microscopical 

 examination of the roots shows that their tips are not provided 

 with root-hairs, while they are very abundantly supplied with 



