HOW PLANTS TAKE UP FOOD MATERIAL 9 



movement in the opposite direction, but since the water 

 moves through the membrane much more rapidly than 

 the molasses or sugar, there is a rapid increase in the 

 volume of liquid on the inside of the funnel. This move- 

 ment through the membrane will continue until the solu- 

 tion on the inside has the same strength or concentration 

 as that on tlie outside. The exchange of liquids through 

 membranes is called osmosis. By this process the fine 

 root hairs of the plant are able to secure a large amount 

 of water from the moist soil. The thin wall of the root 

 hair corresponds to the bladder or parchment membrane, 

 the cell sap to the sugar solution, and the soil moisture 

 to the water in the jar. The sap is more concentrated 

 than the soil solution on the outside of the hair, hence the 

 water in the soil moves through the cell wall just as the 

 water in the jar moved through the membrane and into 

 the sugar solution. 



Sprout some grains of corn and wheat between layers 

 of dark flannel and note the very fine hairs which develop 

 just back of the growing root tip. The moisture which 

 enters the plant through the root hairs carries in solution 

 certain food materials which are essential for the develop- 

 ment of the plant. The moisture passes up through the 

 plant and much of it is evaporated from the leaves after 

 having performed its functions as a carrier of food materials 

 from the soil through the plant to the leaf. The food 

 materials carried by the water are left behind in the leaf 

 where they are combined with substances from the air to 

 form the tissue of the plant, including roots, stems, leaves, 

 and seeds. 



