42 Elementary Principles of Agriculture 



not be absorbed unless the chimney contained the sugary syrup 

 or some similar substance. It will be recalled that syrup is boiled- 

 down sap from cane plants. 



A solution of salt in the chimney would cause the water to be 

 absorbed in the same way as the syrup, because salt, like sugar, 

 makes the solution stronger and denser. Where two liquids are 

 separated by a membrane, more water always goes through into 

 the stronger solution. The bulk of the liquid in the chimney is thus 

 increased, and is forced higher in the chimney. 



67. Conditions Favorable for Root Growth. Not all 



plants require the same conditions for perfect develop- 

 ment. All require some degree of moisture. Some 

 plants do best when their roots are totally submerged 

 in water, as the water-lily. Some land plants will grow 

 with their roots in water, though they do best when 

 the roots are in soil that contains plenty of air as well 

 as water. When roots grow in a moist and very fertile 

 soil, they are short, but have hundreds of little branches. 

 This gives them a large absorptive surface, enabling 

 them to readily take up the water and mineral food. 

 When the soil is poor, or insufficiently supplied with 

 moisture, the roots grow long and slender and have 

 few branches. This does not mean, as some suppose, 

 that the roots are " searching for food. 7 ' When in a 

 fertile soil, roots multiply rapidly, because they are 

 well nourished. When in a poor soil, where the mineral 

 food and water are insufficient, the leaves are unable 

 to supply the roots with enough sugar, oils, proteids, 

 etc., to make the roots multiply and grow rapidly. 

 It has already been observed that roots will not grow 

 vigorously when the oxygen of the air is excluded. Plenty 

 of air is necessary for vigorous growth. 



67a. To Show that Air is Necessary for Root Growth, use two 

 jars, one filled with well-water, as shown in Fig. 28, and the other 



