LEAF MOVEMENTS AND LIGHT 63 



2. Its outline as to main divisions. Of what kind and how 

 many ? 



3. The detailed outline of the margin. 



Compare the mode of veining, or venation, of the elm and 

 the maple leaf by making a diagram of each (see Principles, 

 Chapter X). 



The leaves of elm and of maple agree in being netted veined, 

 i.e. in having veinlets that join each other at many angles, so as 

 to form a sort of delicate lace work. 



Such a leaf as that of the elm is said to be feather veined, or 

 pinnately veined. The maple leaf, or any leaf with closely similar 

 venation, is said to be palmately veined. Describe the difference 

 between the two plans of venation. 



LEAF AEEANGEMENT FOR EXPOSUEE TO LIGHT 



AND AIE; HELIOTEOPIC MOVEMENTS OF 



LEAVES AND SHOOTS 



EXPERIMENT XXVII 



Is the nocturnal position due to removal of the light stimulus or to other causes ? 

 Remove a pot containing an oxalis or a clover plant from a sunny window 

 to a dark closet, at about the same temperature, and note at intervals of 

 five minutes the condition of its leaves for half an hour or more. 



References. Darwin and Acton, 11 ; Pfeffer-Ewart, 31, III ; Detmer- 

 Moor, 9. 



EXPERIMENT XXVIII 



Determination of the values of illumination to produce various leaf positions. ' 

 Select a few common bean plants (Phaseolus) growing vigorously in a sunny 

 place, or a locust tree {Bobinia) at the time in the spring when its leaves 

 have just reached their full size. 



A. Note and sketch the positions of the leaves as follows : 



1. After dusk. 



2. In cloudy daylight or near dusk. 



3. In intense sunlight, near noon. 



1 This is preferably an out-ol-door study. 



