112 



Plant Physiology 



ditions may also be obtained in different greenhouses. Keep 

 an accurate record of the conditions of the experiments, and 

 accompany this with a record of the transpiration data, express- 

 ing the latter ui terms of g m 2 h, as above explained. 



A more accurate evaluation of the factors, and consequently 

 a better conception of the effects of external conditions upon 

 plants, may be obtained by means of experiments continued 

 several days, whilst utilizing, also, autographic recording in- 

 struments. Study the mechanism of the thermograph (Fig. 112) 

 and hygrograph (Fig. 36) ; also set up and standardize some 

 simple evaporimeters (Fig. 31) after the method of Livingston 



[Illustration from Julien P. Friez.] 

 FIG. 36. Hygrograph. 



(section 60) or of Transeau (BoL Gaz., 49 : 459, 1910). Then 

 set up in duplicate with the burette potometers a transpiration 

 experiment (preferably two, under two sets of conditions). 

 This is to be accompanied by the continuous record of tempera- 

 ture and humidity. Make observations upon water-loss as 

 often as possible. The experiment may be continued several 

 days if shoots with woody stems are chosen. Plot and discuss 

 the results. 



