IQ2o] 



SNOW— DIA PHRA GMS 



307 



jar was read on the manometer. It varied somewhat on account 

 of the variation in the flow of the city water supply used to produce 

 the suction. Plants oi 



greenhouse 



its of Scirpus validns, selected from those 

 Cy perns alternifolius ( ?) , already growin 



Experiment i 



This extended February 4-14. The pressure varied between 

 10 and 20 mm. of mercury. This pressure was chosen because air 



Fig. 2. — Apparatus to test effect of low atmospheric pressure: bell-jar 1, control; 

 bell- jar 2, experiment; under each jar a pan of water containing pots of Scirpus; 

 air entering at I and also around bottom of 1 (not sealed as was 2) passed out of 1 into 

 flask where narrowed tube retarded flow and bubbles indicated rapidity of passage; 

 in 2 air entered at bottom and escaped at top, thence through two catch bottles to 

 pump operated by city water supply; m, manometer; w, tube for watering 2. 



a t 20 mm. pressure contains about as much oxygen as is dissolved 

 in water (8). Cy perns would not grow at this pressure, and 

 Scirpus alone was used. The culms were measured twice a day, 

 and, after the close of the experiment, longitudinal and cross sections 

 were made and measurements taken as in the previous experiments. 

 Culms nos. i and 2 belonged to the control plant, nos. 3 and 4 to 

 the experimental plant. Fig. 3 and tables VI and VII give the 



