30 CHEMISTRY, GEOLOGY 



N 



Besides carbonic acid gas, the leaves of plants 

 drink in watery vapor from the atmosphere, 

 which moistens the leaves and stems, and at the 

 same time adds to the substance of the plant. 



Plants take up carbon from the soil in the 

 form of carbonic acid, humic acid, and some other 

 combinations in which it exists in the vegetable 

 matters of the soil (see Appendix, 17) ; and 

 they obtain nitrogen from the soil in the forms 

 of ammonia and nitric acid, which we shall be- 

 fore long describe to our young friends. 



SUBSTANCES IN THE STRUCTURE OF PLANTS. 



Plants are mainly made up of woody fibre, 

 starch, and gluten. The woody fibre constitutes 

 the greater part of every kind of wood, straw, 

 hay, chaff, cotton, flax, hemp, the shells of nuts, 

 etc. 



Starch is first seen in the form of a white 

 powder. Nearly the whole substance of the 

 potato is starch, and nearly half the weight of 



Questions. Do plants drink anything from the atmos- 

 phere besides carbonic acid ? What use do they make of 

 writer ? How do they take up carbon from the soil ? Whence 

 do they obtain nitrogen ? What substances enter into the 

 structure of plants ? What does the woody fibre form ? 

 What is starch ? 



