ABSORPTION. 119 



by the germinating seeds, and the rise of temperature is 

 caused by the oxidation accompanying germination. 



Now it will be seen that plants, like animals, take up 

 oxygen and give off carbonic acid as long as they live, and 

 this process is Bespiration. In this process heat is always 

 set free in plants as it is in the case of animals ; but in 

 plants as the process of heat-production is feeble and other 

 conditions lead to rapid cooling, the rise of temperature is 

 usually insignificant. 



3. ABSORPTION. 



If a flower-pot with a living plant be exposed to the sun 

 without being watered, the plant will begin to droop and 

 wither after a few days. Now if a sufficient quantity of 

 water be given to the plant, it will gradually regain its 

 healthy condition. 



If some living land plants with their roots immersed in 

 pure distilled water be kept for a long time, they will 

 gradually become unhealthy and will finally perish. 



From the preceding experiments it will be found that 

 plants must absorb water and several other substances for 

 the maintenance of their vitality. It is known from several 

 experiments that the food of plants consists of water, solu- 

 ble salts, oxygen, and carbonic acid. 



"Water and soluble salts are absorbed by young roots and 

 root-hairs, oxygen by all living parts, and carbonic acid by 

 all green organs of which leaves are the chief. 



Submersed plants may absorb nutritious substances 

 through their whole surfaces. 



Some insoluble substances as marble are decomposed by 

 the acid sap, which saturates the cell-walls of the root, and 

 are brought into solution. 



