SELECTED BIBLIOGRAPHY 303 



of water per gram of dry weight what per cent of the water originally 

 present has been lost? 



7. Hollow beech trees usually suffer more severely as a result of prolonged 



droughts than those with solid trunks. Suggest possible explanations. 



8. In lumbering practice it has been found that logs of yellow pine and some 



other species float more readily if the side branches are not trimmed off 

 until several weeks after the tree is felled than if they are removed 

 immediately. Explain. 



9. Why should the tearing of the protoplasm away from a cell wall during 



drying usually be more harmful to a plant cell than separation of pro- 

 toplasm from the wall during plasmolysis? 



10. Why do the mature leaves of some species of plants vary appreciably in 



area on days upon which transpiration rates are high while the leaves of 

 other species fail to show such variations? 



11. Plot curves which might reasonably be expected to represent the daily varia- 



tion in the osmotic pressure, turgor pressure, and diffusion pressure deficit 

 of mesophyll cells of a sunflower plant (a) on a "standard day," (b) on s 

 cool, cloudy summer day, (c) on a clear, warm summer day with the 

 soil water content approaching the wilting percentage, (d) on a "standard 

 day" with a heavy thunderstorm in mid-afternoon. 



12. In tomato plants the tip of the main stem is usually the last part to die 



from lack of water, but it is usually the first part to show signs of wilting. 

 Explain. 



13. Plot curves which might reasonably be expected to represent the daily varia- 



tion in transpiration and absorption of water in a corn plant (a) on a 

 "standard day," (b) on an otherwise "standard day" with the soil water 

 content approaching the wilting percentage, (c) on a cool, cloudy day with 

 the soil water content at about the field capacity. 



14. Cite some examples of xeric habitats which occur in regions with a generally 



mesic climate. 



15. Would the time of the day at which mature leaves of a green plant attain 



their maximum water content coincide with the time at which the plant as 

 a whole attains its maximum water content? Explain. 



Suggested for Collateral Reading 



Harris, J. A. The physico-cheinical properties of plant saps in relation to 

 phytogcography. Univ. Minnesota Press. IVIinneapolis. I934- 



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

 George Allen and Unwin. London. 1929. 



Walter, H. Die Hydratur der Pflanze. Gustav Fischer. Jena. 1931. 



Selected Bibliography 



Bachmann, F. Studien iiber Dickenanderungen von Laubblattern. Jahrb. 



Wiss. Bot. 61 : 372-429. 1922. 

 Bartholomew, E. T. Internal decline of lemons. III. Water deficit in 



lemon fruits caused by excessive leaf evaporation. Amer. Jour. Bot. 13: 



102-117. 1926. 

 Chandler, W. H. Sap studies with horticultural plants. Mo. Agric. Expt. 



Sta. Bull. No. 14. 1914. 



