58 ELEMENTS OF PLANTS. 



203. That which causes water, and, with it, these three 

 gases, to enter the plant-cell, is called the Osmotic Power. 



An experiment which any body can make, shows its 

 action. Let some sugared water, in a tube closed below 

 with a film of bladder tied across the end, and open 

 above, be suspended in a vessel of pure water. The 

 liquid in the tube is soon seen to increase by the passage 

 of the pure water upwards through the film. At the 

 same time, some of the sugared water passes through the 

 Him downwards into the vessel. The tube will soon be 

 full and flow over into the vessel, and the double action 

 will continue till the liquids inside the tube and outside 

 are of the same sweetness and density. 



The passage of the fluid from without inwards is called 

 cndosmose ; that from within outwards, exosmose. 



Two gases, of different density, separated by a film, 

 will, in the same manner, pass through it and mingle. 



It is by this power that the various substances that 

 enter a plant not only pass into the cells but also from 

 cell to cell, through all parts of a plant. It is by this, 

 perhaps, that the gases find entrance through the leaves 

 and I lie tender bark of recent twigs. It is by the same 

 power that fluids are thought to pass from cell to cell, 

 through membrane after membrane, in the bodies of 

 animals. 



204. Every part of a plant, even the solid wood, con 

 tains Water, not always in a fluid state, but in such a 

 state that the chemist can separate water, or the elements 

 of water, even from the dryest wood or bark. Water 

 must therefore be supplied to growing plants in abun 

 dance, accordiiiii 1 to the nature of the plant and the season 

 of the year. Without it, iu some form, 110 plant can 

 grow. 



