54 CHAP. Vr. RELATION OF TURGOR AND TENSION 



case described, the increased rate of growth on irrigation 

 with cold water took place after 70 seconds ; but the 

 responsive growth-elongation after application of warm 

 water occurred in less than 20 seconds. 



In regard to the effect of irrigation with warm water, 

 certain precautions have to be taken, for sudden application 

 of hot water is liable to induce excitatory contraction : it 

 is therefore advisable to commence irrigation with tepid 

 and end with warm water. The transport of warm water 

 to the growing region may, however, introduce a complica- 

 tion of enhancement of growth by the rise of temperature. 

 This uncertainty may be obviated by waiting for the tissue 

 to return to the temperature of the room. The persistent 

 rate of growth may then be regarded as solely due to the 

 enhanced activity of the ascent of sap. 



Experiment 29. Temporary and persistent enhance- 

 ment of growth. — The results obtained with the peduncle of 

 Zephyranthes will be found to be of interest in this con- 

 nection. Its rate of growth under partial drought was 

 found to be • 04 [X per second ; application of warm water 

 increased the rate to 0-20 [x per second. After 15 minutes 

 the rate fell to 0-13 [i, and after an hour to the permanent 

 rate of • 08 [x per second. It will be noted that even then 

 it was twice the initial rate before irrigation. 



I give below a table which shows the immediate effect 

 on growth of irrigation with cold and with warm water, 

 the persistent effect being given in Table IV : 



Table III. — Effect of Irrigation with Cold and 

 WITH Warm Water. 



