248 THE SECOND BOOK OF BOTANY. 



the water, contain liquids denser than that which 

 surrounds them, and hence the flow is from without 

 inward. When they have thus been filled with water, 

 the liquid they contain is so related to that of the next 

 inner cells that it passes on by osmotic action, thus 

 relieving the outer cells, when they are again ready 

 for a fresh supply from the soil. In this way the ac- 

 tion is kept up, from cell to cell, till the liquid has 

 traversed the entire substance of the plant, from the 

 tips of the roots to the uppermost leaves. 



The third agent in causing the absorption of 

 liquids by plants is, the evaporation of water by the 

 leaves, and its consumption by the growing buds, 

 which tends to produce a vacuum in the uppermost 

 tissues. So that the principle of suction here comes 

 in play to pump up the materials of the soil into the 

 body of the plant. 



In germination, the food of the plant is furnished 

 by the albumen of the seed, or by the gorged coty- 

 ledons of the embryo itself, as in peas and beans. 

 This food is changed from the insoluble to the soluble 

 state by the action of warmth and moisture ; is dis- 

 solved, and, by capillary and osmotic action, is carried 

 into the radicle, and used by the growing cells in the 

 development of the plumule and the roots. By the 

 time this supply is exhausted, the growing plantlet is 

 able to live upon material furnished by the soil. Its 

 first food is the starch, and other substances stored 

 up in the seed the year before, and is organic mat- 

 ter. But the substances taken from the soil, dis- 

 solved in water, are carbonic acid, ammonia, and 

 earthy and alkaline salts mineral matters which 

 cannot serve in building up the plant's fabric ; these 



