FOOD. 83 



acid gas, and tbp plant's healthy assimilation of carbon, it 

 is during the day that carbon is absorbed and oxygen lib- 

 erated. There is no chemical action of plants at night. 

 Sunshine is necessary for their work. The night, therefore, 

 brings to them that rest which it does to almost all ani- 

 mated nature. 



217. Besides these four primary organic elements, plants 

 absorb various substances from the soil, as sulphuric acid, 

 magnesia, potash, lime, alumina, chlorine, iron, etc. These 

 are converted into liquids by the action of spongioles, 

 so as to enable the plant to draw them up in the shape 

 of sap. 



218. The process by which the plant then assimilates 

 this food thus prepared is called chemical action, differing, 

 however, very materially from inorganic chemical union, 

 inasmuch as no art has been able to imitate it, requiring 

 as it does the action of life. 



219. A chemist can analyze a glass of water, and show 

 you the two gases, hydrogen and oxygen, in their original 

 elementary form ; he then can recombine them and present 

 them to you again under the form of water. The same 

 chemist can take a plant, and in his laboratory reduce it to 

 its component elements, and tell you to a fraction what 

 gases, liquids, solids, acids, alkalies, etc., and in what quan- 

 tities, enter into its composition. But this is all he can do. 

 He cannot convert them back into a plant. This can 

 only be accomplished through the mysterious agency of 

 what w^e call the principle of life, the secret of wiiich is hid 

 from us in a cloud of impenetrable mystery. You see that 

 organic chemistry requires the action of living organs, 

 while inorganic chemistry combines its elements by a 



217. Besides the four elements, carbon, oxygen, hydrogen, and nitrogen, what 

 other substances do plants absorb ? and how ? 



218. How does organic chemistry differ from inorganic ? 



219. Tell me what a chemist can do with a glass of water. Can he do the 

 same with a plant ? Why cannot he make a plant if he has all the component 

 parts ? 



