AUTONOMIC MOVEMENTS IN SUCCULENTS 309 



growth in the open. The next experiment records the influ- 

 ence of other combinations of environmental factors upon the 

 movement. 



Experiment 8. 



Object: An investigation of the influence of light and temperature upon the day 

 and night movements, by means of their measurement under conditions of (1) 

 constant high temperature with an alternation, at twelve hour intervals, of diffuse 

 light and darkness; (2) constant high temperature with an alternation of sunlight 

 and darkness; (3) constant low temperature with an alternation of diffuse light 

 and darkness; (4) constant low temperature and constant darkness; (5) constant 

 darkness with an alternation every twelve hours, of high and low temperatures. 

 For the high temperatures 90° to 100° F. were selected and for the low ones 

 55° to 60° F., the idea being that these represented the average maximum and 

 minimum to which plants are normally subjected. Thus any metabolic changes 

 which might influence the movements would still appear. 3 



Material: Plants Nos. 1, 2, 4, and 7. Nos. 1 and 2 were green-house raised 

 plants; Nos. 4 and 7 were from the open. 



Method: The constant high temperatures were obtained by placing the potted 

 plants within glass cages (about 15 cubic feet capacity) which were fitted with 

 electric heaters and automatic controls. The temperature between the top and 

 bottom of the cages varied from 1° to 1.5° F., while at a given level the variation 

 was no greater than 0.2° F. The thermograph was placed at the mean level of the 

 aerial parts of the plants. For the constant low temperature, a vault beneath 

 the laboratory was used. No means was at hand for obtaining a constant low 

 temperature in sun-light. Unless statements are made to the contrary, the 

 plants used were at nearly maximum turgidity and were in wet soil. 



Results: The movements are recorded in the form of graphs in figures 4-6. 

 Light and temperature changes are indicated in the same manner as in previous 

 experiments. 



When the behavior of the plants is examined from the graphs 

 the following facts appear. The characteristic upward and 

 downward movements for day and night cease entirety under 

 conditions of (1) constant high temperature with an alternation 

 every twelve hours of darkness and diffuse light; (2) constant 

 high temperature with an alternation of darkness and sunlight ; 

 (3) nearly constant low temperature with an alternation of dark- 



3 It was thought when these conditions were planned that acidity changes 

 within the plant could be predicted from the work of H. M. Richards (Acidity 

 and gas interchange in cacti. Carnegie Inst. Pub. 209), and G. Krause (Die 

 Wasserverteilung in der Pflanze. Abhand. d. Natrfor. Ges. Halle, 16, 143). But 

 later, when acidity determination were made on the material under these con- 

 ditions, the results showed that further work must be done on acidity relations 

 before such predictions can be made with any degree of accuracy. 



