172 THE LOSS OF WATER FROM PLANTS 



Discussion Questions 



1. How could you demonstrate experimentally that a much larger quantity of 



water is lost by stomatal transpiration in most species than by cuticular 

 transpiration? 



2. Is it harmful to prune grapevines or other woody plants when they will bleed 



profusely? 



3. Explain how a mercury valve (Fig. 38) works in preventing entrance of rain 



into an atmometer reservoir. 



4. When a leaf in bright light is surrounded by a bag of cellophane, which 



checks transpiration, the temperature of the leaf rises rapidly. This has 

 been interpreted as indicating that rapid heating of a leaf would occur 

 if transpiration ceases. What is a more probable interpretation of this 

 effect? 



5. When computing transpiration per unit area of leaf surface should both upper 



and lower epidermis be considered as evaporating surfaces or only one? 



6. What method or methods of measuring transpiration would you recommend 



for determining: (a) the transpiration rate of single leaves from various 

 heights on the same tall oak tree? (b) the relative and absolute amounts 

 of stomatal and cuticular transpiration of a potted plant? (c) the effect 

 of high and low humidity upon the transpiration of potted geranium plants? 

 (d) the transpiration of small plants growing in a solution culture? (e) the 

 effect of oil sprays on the transpiration of peach trees? Explain reasons 

 for your choices. 



Suggested for Collateral Reading 



Burgerstein, A. Die Transpiration der Pflanzen. I, II, and III. Gustav 



Fischer. Jena. 1904, 1920, 1925. 

 Fames, A. J., and L. H. MacDaniels. An introduction to plant anatomy. 



McGraw-Hill Book Co. New York. 1925. 

 Hayward, H. E. The structure of economic plants. Macmillan Co. New 



York. 1938. 

 Maximov, N. A. The plant in relation to ivater. Edited by R. H. Yapp. 



George Allen and Unwin. London. 1929. 



Selected Bibliography 



Briggs, L. J., and H. L. Shantz. An automatic transpiration scale of large 

 capacity for use with freely exposed plants. Jour. Agric. Res. 5 : 117- 

 132. 1915. 



Brown, H. T., and F. Escombe. Researches on so?ne of the physiological proc- 

 esses of green leaves, etc. Proc. Roy. Soc. (London) B. 76: 29-137. 

 1905. (4 papers.) 



Curtis, O. F. What is the significance of transpiration? Science 63: 267- 

 271. 1926. 



Freeland, R. O. Effect of transpiration upon the absorption of ?nineral salts. 

 Amer. Jour. Bot. 24: 373-374- i937- 



