Sampson and Allen: physical factors on transpiration. 49 



inches. All were placed under bell jars. An aspirator was used to 

 reduce the pressure, which was measured by an accurately adjusted 

 aneroid barometer. AJl other factors were uniform and constant, 

 so that variations in transpiration were caused only by the differ- 

 ence in pressure. 



TABLE VIII. 



PRESSURE LOSS CHECK 



Normal 



I 28.9 in. 2.57 2.64 



2 28.9 in. 2.61 2.59 



3 20. in. 3.43 3-41 



4 20. in. 3.50 3.48 



5 15- in. 3-6i 3-6o 



6 15- i". 3-56 3-53 



These experiments, showing transpiration to be increased by a 

 decrease in atmospheric pressure, contradict the theory of Bonnier, 

 J. e., that the increased transpiration in high altitudes is due to 

 increased light intensity. (Compt. rend, de I'acad. des sc. Paris torn. 

 CXI, 1890, II, p. 377.) 



Transpiration of Scirpus lacustris. 



A number of bog plants, because of their great reduction of leaf 

 area and general external appearance, have been called bog xero- 

 phytes (Schimper, p. 17), in spite of the fact that a xerophyte is 

 a dry soil plant and that these plants grow in a super-saturated 

 soil. Such a plant is Scirpus lacustris, and it has afforded most 

 interesting results. 



These plants were taken from the edge of a pond during the win- 

 ter and placed in earthern pots in the plant house. In order to pro- 

 vide conditions as nearly like those of the natural habitat as pos- 

 sible, the pots were submerged in an aquarium. When they had at- 

 tained a growth of about one meter in length they were removed 

 from the aquarium, their transpiration measured, and the following 

 results obtained : 



TABLE IX. 



