[Pkoc. Roy. Soc. Victoria, 28 (N.S.), IN., II., 1916]. 



Art. XX. — The Influence of Gaseous Pressure on Growth. 

 (Preliminary Communication). 



By ETHEL McLENNAN, B Sc. 

 [Read 9th December, 1915]. 



The British Association for the Advancement of Science granted 

 the sum of £50 for the purpose of carrying out a research, " On 

 the Influence of Varying Percentages of Oxygen, and of Various 

 Atmospheric Pressures upon Geotropic and Heliotropic Irritability 

 and Curvature." 



This sum was expended on apparatus necessary for the above 

 research, which, for the most part had to be obtained from England, 

 and some delay was experienced owing to difficulties arising from 

 the war. In consequence work so far has been mainly of a pre- 

 liminary character, but a description of the apparatus employed 

 and a summary of the results obtained to date may be of a littlu 

 interest. 



According to Pfeffer (Pfeffer's Physiology of Plants. Vol. II., p. 

 114): — " A mere rise of gaseous pressure, if sufficiently great, will 

 produce a retardation and ultimate cessation of growth. 1 ' 



He explains this by stating that a high gaseous pressure outside 

 the plant will antagonise turgor. This could only lie a temporary 

 effect, since the protoplasm and the cell wall are permeable to oxygen 

 and nitrogen in solution, so these gases will pass through until the 

 partial pressure of the dissolved gases inside the cell produces an 

 increased osmotic pressure corresponding to the increased gaseous 

 pressure outside the cell, thus producing a gaseous equilibrium. 



Jaccard (Rev. Gen. d.Bot., 1893) states that growth in air at from 

 ."'-() atmospheres, is not retarded, and may even in some cases be 

 accelerated. 



In order to test these results and those of other observers, I have 

 been performing some experiments under more favourable con- 

 ditions than was previously the case. It is important that the 

 observations should be made under conditions where immediate 

 responses can be observed in short intervals of lime; this can only 

 lie done by the aid of the horizontal microscope watching the growth 

 of seedlings in a pressure chamber. 



I I R P A P V I _ 



