Influence of Gaseous Pressure on Growth. 2 17 



Not only does a fluctuation in the temperature affeci the rate of 

 growth, but also some seedlings appear to have inherently a highei 

 rate of growth than others. Nevertheless, the effect of raised gaseous 

 pressure is a relatively constant one, irrespective <>t' temperature or 

 of the inherent rate of growth of the seedling. 



The seedlings used for all the experiments have been Pimm arvense 

 (field pea), and so far as possible 1 have chosen those of about equal 

 age and size. 



Whether the retardation caused by increased gaseous pressure is 

 due to an increase in the partial pressure of the dissolved oxygen 

 or not has still to be determined. 



Jentys found that oxygen under a pressure of from .'5-4 atmo- 

 spheres (= the same density as in air under a pressure of from 

 14-19 atmospheres) caused retardation of growth. 



Since, however, air under 3-4 atmospheres pressure produces a 

 similar retardation this is not due wholly to the increased oxvgen 

 pressure, but is due in part at least to increased gaseous pressure. 



Summary of Results. 



I. — Average rate of growth in air = .275 mm. per hour. 



IT. — Atmospheric Air + 15 lbs. 



Temp. Rate of growth per hr. 



°C. ram. 



(a) Beginning of experiment 16 .32 

 End of 1st day - - - 16 - .25 



/. retardation = .07 in 1 day. 



(b) Beginning of experiment - 14 - .192 

 End of 1st day - 16 - .097 



/. retardation = .09-"> in 1 day. 

 III. — Atmospheric Air + 30 lbs. 



Temp. Rate of growth per hr. 



°C. mm. 



(a) Beginning of experiment 13.5 - .25 

 End of 1st day - 14 .128 



.*. retardation = .122 per hr. 



(b) Beginning of experiment 15 - .448 

 End of 1st day - 14 .32 



.'. retardation = .128 



