130 



PHYSIOLOGY OF NUTRITION. 



52 C. for 10 minutes. On the contrary, death may not take place 

 for days. The newly matured leaves gradually become discoloured, 

 while the older leaves, the internodes and also the buds do not 

 perish till later. In carrying out exact comparative investiga- 

 tions as to the influence' of high 

 temperatures on plants, it is neces- 

 sary to repeat the experiment at 

 any particular temperature several 

 times, using also each time a fresh 

 and perfectly normal plant. In this 

 way we avoid errors. It would also 

 be instructive to leave plants in the 

 thermostat for a longer period (several 

 hours or even days) at comparatively 

 low temperatures, e.g. 35-40 C., and 

 observe their subsequent behaviour. 



Plants suffer if exposed for ten 

 minutes, or somewhat longer, to a 

 temperature of 52 C. in air, but 

 exposure for ten minutes to tempera- 

 tures of from 45-48 C. causes their 

 death, if their environment is water 

 instead of air. To demonstrate this 

 fact, we invert a potted plant (laying 

 strips of wood over the top of the 

 pot to prevent the soil from falling 

 out), and plunge the aerial part of 

 the plant into water at the tempera- 

 ture in question. The temperature 

 is kept constant during the experi- 

 ment, and at the end of ten minutes 

 we remove the plant from the water, 

 and observe its farther behaviour. 



In studying the influence on plants 



the influence of high temperature oii of water at high temperatures, we 



may also experiment with organs 



severed from the plant, e.g. leaves. I have used, e.g., leaves of 

 Begonia manicata and Vitis vinifera, which are very suitable 

 because they undergo a marked change in colour when their 

 cells die. If we immerse leaves of Begonia for fifteen minutes in 

 water at a temperature of 40 C., their cells do not die. When 



FIG. 44. Apparatus for investigating 



