NUTRITION OF CELLS. 239 



The nutrition of the plant is accomplished by means of a 

 peculiar property of the membrane which forms the wall of 

 the cell. This property consists of a power of the cell mem- 

 brane to combine with the fluid in contact on one side of it, 

 and to decompose it, and thus pass it out on the* other side 

 of it; or to transpose it in some way through its substance. 

 Thus if a piece of wet bladder is tied over the end of a tube, 

 and the tube is filled to a certain height with alcohol and 

 then immersed in water, the water immediately begins to 

 pass through the bladder and mingles with the alcohol; 

 while the alcohol passes through the bladder and mixes with 

 the water on the other side of it. The same movement takes 

 place with solutions; but the cell membrane has the power 

 of retaining what it requires for the nutriment of its con- 

 tents; and building up its own tissue; and then of permit- 

 ting the transmission of the remainder through its walls to 

 the next cell. In this way the water of the soil containing 

 in solution the food which the plants require, is absorbed 

 through the cells of the fine feeding roots, and is passed 

 through from one to another of the many millions existing 

 in the plant, until it reaches the leaves; when, disburdened 

 of its load of nutriment which is all absorbed by the cells, 

 it passes off through the pores of the leaves by evaporation 

 into the outer air. 



Cells are the minute factories of the universe, in which 

 the vast forces which we call Life are constantly operating 

 to change and transform inorganic matter into organized 

 structures, by means of a constant flow and transmission of 

 fluids through them. The force by which these fluids are 

 transported from the distant termination of a root to the 

 uttermost leaf at the top of the highest tree, is the delicate 

 one above described, and is called osmose. What the power 

 is by which the matter in solution is changed into organized 

 living and moving substance we know not; but we call it 

 vital force, and although its action is imperceptible to us 

 except by its results, yet the power exerted is so enormous, 

 that each pound of carbon fixed in the substance of a crop, 

 requires an equivalent of power which is sufficient to raise 



