76 THE PRINCIPLES OF AGRICULTURE. 



obtain food from the soil? Explain the principle of diffusion. 

 What causes substances to mingle and dissolve so readily ? Ex- 

 plain osmose. How are liquids, and substances dissolved in them, 

 able to pass through a membrane ? To what fact is the term cap- 

 illary attraction applied? Why is it so named? Why will a 

 whole towel become wet if one end is placed in water ? Why will 

 water rise higher in a very small tube than in a larger one ? 



How, according to these principles, do the substances of the soil pass 

 into plants ? What effect is produced upon plants by the attrac- 

 tion of their roots for water ? Why does a plant droop when the 

 soil becomes too dry ? 



Of what do the roots, stems, and leaves of plants consist ? In what 

 way is growth produced ? Name some plants composed of loose 

 cells. What is vegetable tissue ? What is the form of cells in 

 different plants ? 



Explain how moisture reaches all parts of the plant ? What two 

 causes tend to keep up a continuous flow of sap? How does the 

 moisture of sap escape into the atmosphere ? Why does sap flow 

 slowly in damp weather? Explain the cause of the abundant flow 

 of sap from the maple in the spring ? Why does the flow cease as 

 soon as the leaves begin to grow ? Does the flow of sap resemble 

 the circulation of the blood of animals? 



In what direction do the nutritive substances move within the plant ? 

 What causes them to move ? Can plants choose their food? 



What is the natural purpose of the growth of plants ? Name the 

 different parts of a flower. Explain the purpose of the pistils 

 and the stamens. Name some plants that have only one of these 

 upon a single plant. Name some that have the two upon differ- 

 ent parts of the same plant. How are many different varieties 

 of the same species of plants obtained ? AVhy will not peas and 

 beans mix and produce new varieties ? 



