EXERCISE 25 (Continued) 



to be in shadow. How much unoccupied wall surface is visible 

 between the leaves. According to your calculations, what per 

 cent efficient is the plant in intercepting the light which comes 

 to the part of the wall occupied by the plant ? 



4. May leaves be arranged to receive less than the maximum 

 amount of light? 



Examine plants of prickly lettuce growing in the bright sun- 

 shine. Do the surfaces of the leaves face upwards ? What is 

 their characteristic position ? What effect would this position 

 have upon the intensity of illumination on the leaf surfaces at 

 noon on a bright summer day ? 



If the compass plant (iSilphium laciniatum or 8. integrifolium) 

 grows in your vicinity, examine it also. Why has it been called 

 the compass plant? 



References 



BERGKN and CALDWELL. Practical Botany, pp. 55-65. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 69~77. 

 Longfellow's " Evangeline," 11. 1216-1221, refers to the compass plant. 



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