LABORATORY MANUAL 35 



(7) What, then, is the chief agent in keeping young stems 

 rigid? 



(8) Each group constitutes a leaf. How many leaves are 

 there on your plant? 



(9) Do the leaves shade each other much or little? 



(10) How does the arrangement of leaves on the stem 

 affect the shading? 



(11) Hold the leaf up to the light and describe the distribu- 

 tion of veins. 



(12) Describe a cell from the interior of a leaf -as seen 

 under the compound microscope. (This should be arranged 

 by the teacher.) 



(13) Examine with the microscope a portion of the exterior 

 of the leaf, showing the leaf pores. Describe what you see. 



EXERCISE XXVII (Textbook 301) 

 ONE FUNCTION OF LEAVES 



MATERIALS: A plate or saucer; leaves from a growing 

 plant; balances; a thin sheet of rubber; a potted plant; 

 a glass jar or a box with one glass side, large enough to 

 cover the plant. 



DIRECTIONS FOR WORK: 



(1) Weigh the dish. Place several leaves from a growing 

 plant in the dish and weigh them together, to .1 g. Leave 

 the dish uncovered in a moderate temperature for 24 hours 

 and weigh again. Continue this for several days, recording 

 each weight taken. 



(2) Cover the pot and the earth around the stem of a 

 growing plant closely with a sheet of rubber. Place the 

 plant thus prepared under a dry glass cover and leave it 

 standing. From time to time, observe any change occurring 

 under the glass. 



If the plant is in a warm room, cool the glass after 24 



