CELLULAR ANATOMY OF THE LEAF 215 



41. What is the cellular structure of a typical leaf? 



(1) What is the structure of the starch- 



making system ? 



(2) Of the conducting and strengthening 



system ? 



(3) Of the aeration system? 



(4) Of the protective system ? 



Answer by a study of the Rubber-plant (Ficus 

 elastica) leaf. Observe carefully the characters 

 of the leaf as a whole ; then cut thin cross- 

 sections with your scalpels and compare with 

 the prepared sections. 



All of the systems should be represented in a 

 single drawing. 



42. It is a well-known fact that leaves give off into 



the air considerable quantities of water. It is 

 desirable to measure exactly how great the 

 quantity is for an ordinary plant under normal 

 conditions, and also how the rate of this giv- 

 ing-off, or transpiration, is affected by changes 

 in the external conditions. To determine it, the 

 most exact method is weighing, and to employ 

 this, it is necessary to use a potted plant 

 in which all evaporation is prevented, except 

 that through the leaves and stem. This has 

 been done in Experiment 7. 



(i) What amount of water may be given off 

 by a plant under normal conditions, 



