CHAPTER XVI 

 RELATIONS OF PLANTS ABOVE THE GROUND 



148. We have now found out a few things about the 

 relation of the plant to the soil. Soil culture, we found 

 to be making a home for the roots. What can we do to 

 make the conditions above the ground more favorable 

 to the growth of the crops? 



149. Provide for Leaf Development. All the carbon 

 in plants, which is fully half their substance, is absorbed 

 from the air by the green leaves, and, through the agency 

 of sunlight, made into plant substance. The leaf is a 

 part, or organ, where the raw materials are brought 

 together and made into the foods that nourish the plant. 

 It is plain, then, that in husbanding plants provision 

 should be made for normal leaf development. Leaves 

 will not grow unless plenty of light is present. This is 

 shown when plants are grown in darkness. We have 

 often noticed how the leaves arrange themselves so that 

 they get the greatest benefit from the rays of light. 

 Plants growing beside a wall or in a window turn their 

 leaf surfaces toward the light. Vigorous leaf develop- 

 ment is possible only when plants are far enough apart 

 to not unduly shade each other. Too many plants must 

 not be allowed to grow on the same ground, whether 

 they be weeds or all of the crop planted. When the 

 plants are too close together, the leaves and side branches 

 do not grow, and the stem spindles up in an effort to 

 reach the best light. The individual plants are thus 

 weakened, and are more subject to the attack of insects 



(103) 



