THE LEAF AND ITS FUNCTIONS 87 



38. Wliat various functions may stipules i:»crform? 



39. Give the number of stomata found per square centimeter of leaf 

 surface on three species of plants. 



40. What is the composition of ordinary air? 



41. How many cubic centimeters of air are needed to provide enough 

 carbon dioxide for the manufacture of one gram of starch by photosynthesis? 



42. About what proportion of the energy reaching a leaf in sunlight is used 

 in the process of photosynthesis? How does this compare with the amount 

 utilized by a good steam-engine from the burning of coal? 



43. About how much sugar is normally manufactured by one square meter 

 of leaf-surface of an average plant during an average summer's day ? 



44. Are the leaves of "foliage-plants," which are brightly colored (not 

 green) able to carry on photosynthesis? Explain. 



45. In the case of some one common crop-plant, give the percentage of 

 dry matter, of water, and of ash which typically compose it. From what 

 source has each been derived? 



46. When and by whom was the process of photosynthesis in plants first 

 clearly understood? 



47. What is the average annual rainfall in this region? About how much 

 of this is returned to the air by a vigorous crop through transpiration? 



48. Give the derivation of the following terms and explain in what way 

 each is appropriate: 



Petiole Stoma Xanthophyll 



Epidermis Photosynthesis Chloroplast 



Mesophyll Chlorophyll Transpiration 



