LEAVES AND THEIR FUNCTIONS 



125 



the bud in the axil of the leaf, that is, between the leafstalk 

 and the branch; (2) by the presence of stipules (this is well seen 

 in the rose leaf) ; (3) by the fact that the arrangement of veins in 

 the leaflet frequently does not follow the same system of branch- 

 ing as would be found in a simple leaf of the same form. 



Arrangement of Veins. — The shape of the blade of leaves of 

 dicotyledons depends somewhat upon the arrangement of the 

 veins. If the blade is long and thin, the veins will be found to 

 go out from the midrib somewhat like the side parts of a 

 feather; hence the leaf is said to be 

 feather veined (or pinnate). If the blade 

 is nearly circular in outline, the veins 

 will leave the petiole to radiate some- 

 what like fingers from the jDalm of the 

 hand. Such venation is said to be pal- 

 mate. 



The same general arrangement of veins 

 holds true for compound leaves. The 

 pea and locust are examples of pinnately 

 compound leaves, the horse-chestnut of 

 a palmately compound leaf.^ 



Leaves turn toward the Light. — It is 

 a matter of common knowledge that green 

 leaves turn toward the light. Place 

 growing pea seedlings, oxalis, or any 

 other plants of rapid growth near a win- 

 dow which receives full sunlight. Within 

 a short time the leaves are found to be 

 in positions to receive the most sunlight 

 possible. 



Home Experiment. — Turn such plants after two or three days so that 

 the leaves are away from the sun. Make observations every hour during 

 some Saturday morning and try to find out just what part of the leaf turns 

 to the Kght. 



Effect of Light. — We have already found that seedlings grown 

 in total darkness are almost yellow-white in color, that the leaves 



' For laboratory work on leaves, see Hunter and Valentine, Manual, pages 39-47. 



The skeleton of a pinnately 

 veined leaf; M.R., midrib; 

 P., the leafstalk or petiole; 

 v., the veins. 



