230 STRUCTURE AND VITAL PROCESSES OF PLANTS 



hairs than separate the mud particles from the hairs. Now 

 what may tlie function of these root-hairs beV 



Take a test-tube and fill it with a saturated lotipn of salt or 

 sugar, stained red by eosin. Close its mouth by means of moist 

 parchment paper, taking care that no air bubbles are left in the 

 test-tube. This apparatus is now immersed in a dish with rain 

 water. After about twenty-four hours it will be observed that 

 the parchment paper is bulged out considerably and that the 

 rain-water is red, thus indicating not only that some of the rain- 

 water must have passed through the parchment paper increasing 

 the quantity of liquid in the test-tube, but also that some of the 

 red salt solution must have passed out. However, the fact that 

 the parchment paper is bulged out shows that the quantity of 

 liquid that has passed into the test-tube is larger than vice versa. 

 This physical phenomenon is called Osmosis. It must be said 

 that the experiment will be successful only if the two liquids are 

 separated by a porous wall, and if they are of different densities. 

 Let us now apply the law underlying this phenomenon to wliat 

 we have learnt of the root-hairs. The root-hairs, the walls of 

 which are porous membranes, contain an acidulous liquid, which 

 may be proved by means of litmus paper in which a root-tip 

 with root-hairs is squeezed. Moreover, each particle of earth is 

 surrounded by a film of moisture. The presence of such moisture 

 can be shown in the following way: heat dry earth in a fiat 

 dish, placing a glass plate over the dish. After a short time the 

 moisture contained in the earth and dissipated l)y the heat will 

 be found hanging from the glass plate in drops. If the earth 

 is thoroughly dried, and the same experiment repeated after the 

 earth has been exposed to the atmosphere for tsome time, moisture 

 may again l)e discovered on the glass-plate. Now, this moisture 

 passes through the walls of the root-hairs, and a small quantity 

 of the acid inside the cells ])asses out and helps to dissolve the 

 minerals of the earth. The quantity of moisture absorbed by 

 the root-hairs Ijeing greater than the (quantity of li(|uid secreted 

 by them, the root-hairs become turgid. In tlic same way the 

 liquid food is passed on from cell to cell in the body of the plant, 

 the cells high up boing filled with n denser coll-li(|uid than those 



