4.6 THE LEAF 



LEAF ADJUSTMENT 



Material. — Upright and horizontal twigs from the same plant, any 

 kind obtainable. A potted plant of oxalis, spotted medick, white clover 

 or Japan clover (Lespedeza striata), or any other irritable kind. 



54. Leaves adjust themselves to Light. — • Take two 

 sprigs, one upright, the other horizontal, from any con- 

 venient shrub or tree — those with opposite, or two-ranked 

 leaves, like the elm and linden will generally show this 

 peculiarity best — • and notice the difference in the position 

 of the leaves. - Examine their points of attachment and see 

 how this is brought about, whether by a twist of the petiole 

 or of the base of the leaf blades, or by a half twist of the 

 stem between two consecutive leaves, or by some other 



87 



86, 87. — Adjustment of leaves to different positions: 86, upright; 

 87, procumbent. 



means. Observe both branches in their natural position ; 

 what part of the leaf is turned upward, the edge or the 

 surface of the blade .' Change the position of the two 

 sprigs, placing the vertically growing one horizontal, and 

 the horizontal one vertical. What part of the leaves is 

 turned upward in each .' One need only glance at the 

 sky on any bright day and see how the light falls to 

 understand the meaning of this adjustment. Would the 

 same amount of light and air be secured by any other .-' 



Rose bushes and a few other plants sometimes take on 

 a second growth in late summer and autumn. If you can 

 find such a plant, bend a young vertical branch into a hori- 

 zontal position, and a horizontal one into an upright position 

 and fasten them there. Examine at intervals and note the 

 adjustment of the new leaves as they develop. 



