NATUBE-STUDT LESSONS. 121 



D. The Eelation of the Position of the Leaf to the Light. 



34. {a) Examine the leaves of an erect, unbranched 



plant such as the mullen. 



{b) What is the position of the lower leaves rela- 

 tive to the stem ? 



(c) What are the positions of the leaves higher 

 up the stem? 



{d) What would be the effect on the amount of 

 sunlight received if all the leaves had the 

 horizontal position of the lowest leaves ? 



35. What adaptation of the leaf to sunlight is effected 

 in this plant? 



36. Compare the leaves on the same muUen-stem as to 

 size. 



37. What adaptation to environment is evident in this 

 difference of size ? 



38. Make similar observations of the shepherd's-purse. 



39. Make a list of plants in which you have discovered 

 similar adaptations. 



40. {a) Examine the leaves of the prickly-lettuce or 



wild-lettuce. 

 (b) How does their position relative to sunlight 



compare with that of the mullen? 



{c) Account for this modification. 



Modifications such as these are not due to accident, but are rather definite 

 modes of adjustment to environment. 



E. Belation between Width of Leaf-blade and the Number of 

 Vertical Whorls on an Erect Stem. 



41. {a) Examine the leaves of the sunflower and the 



lily. 

 (b) Compare their leaves as to the following :— 

 (i) Proportionate length of blades. 



(2) Width of blade. 



(3) Mode of attachment 



