256 AGRICULTURE. 



rich soil) for the sand; select the plants, and label the 

 pots as in above experiment. 



() When watering the plant in pot No. 2, add a small 

 but definite amount of water leeched from wood ashes; 

 when watering the one in pot No. 3, add the same 

 amount of water leached from stable compost; when 

 watering pot No. i, add the same amount of each. As 

 above, the condition of the plants must determine the 

 time and amount of the food-supply. 



(c) Make the same observations and comparisons as 

 in Experiment 26 (/). 



($) Light is another factor in inducing vari- 

 ation among plants. Light, in some degree, is 

 essential to the growth of all green plants. 

 Hence, all such plants strive to adapt themselves 

 with reference to their light relations (#) in 

 the arrangement of their leaves by the rosette 

 habit (Fig. 81), as in the plantain and dande- 

 lion; (^) in the manner of branching and leaf- 

 arrangement of trees; (V) in the elongation of 

 and direction of the stems, as in the trees and 

 vines of a dense forest; or ( <? r ) by turning to- 

 ward the light, as in the sunflower. 



EXPERIMENT 28. The student should be required to 

 make actual observations and measurements of the 

 variations of plants for adaptation to light from those 

 plants of the same kind grown in the light and in the 

 dark or partial darkness. 



EXPERIMENT 29.* Let him try to produce a voluble^ 

 stem by starting some erect plant as, the potato or 

 tomato in a darkened place, so arranged that light is 

 admitted only from one small opening (about three 

 inches square) at one side and above the plant. When it 



