120 RESPIRATION 



ionized by polonium deposited on copper foil. The ionized air 

 was supplied for one hour, intermitted for one hour and then 

 again supplied for one hour. There always obtained an in- 

 creased respiration, the greatest percentage observed being 

 29-11 ± 5-62 during the second period. This acceleration 

 varies according to the degree of ionization : with air ionized 

 20,000 times above that of the surrounding air, an in- 

 creased rate followed each application of the polonium ; with 

 100,000 times that of normal air a markedly significant in- 

 crease obtained in the second period only, and when the air 

 was ionized a million times there was no significant increase 

 in respiration. Similar results were obtained by Whimster * 

 with the leaf of Pelargonium zonale, who found a percentage 

 increase of 857 ± T l XXi tne respiration rate at 25 C. in air 

 ionized from 364 to 728 times that of normal air. The reason 

 for the difference is not obvious : ionized oxygen is more 

 potent than deionized oxygen so that the ionized oxygen of 

 the daytime air, according to Spoehr, possibly accelerates 

 the purely oxidative process of respiration, not the initial 

 disruption of the respirable material. But until it can be 

 said with certainty at what stage in respiration oxygen becomes 

 operative, an adequate explanation is not possible. 



CONDITIONING FACTORS. 



TEMPERATURE. 



In general terms an increase in temperature results in an 

 increase in the respiratory activity until death takes place. 

 The following figures, given by Matthgei,| represent the mean 

 value of carbon dioxide evolved by 2 grams of cherry laurel 

 leaf per hour at the temperature specified : — 



The inspection of these figures shows that for the low and 

 medium temperatures employed there is a gradual increase in 



* Whimster : "Ann. Bot.." 1927, 41, 357. 



f Matthaei : " Phil. Trans. Roy. Soc," B, 1904, 197, 47. 



