310 Mr. A. J. Wilmott. Experimental Researches on 



160 ■ 



dLUtiUed 



s (0 ,15- ao 

 'm.t.uu.te^ 



Fig. 2. 



,FiG. 3. 



Fig. 2.— Initial oxygen diffusion effect plotted from Angelstein's experiments. Four 

 solutions, respectively distilled water, dilute KHCO3, dilute KgCOg, and tap water, 

 were allowed to stand in shallow dishes in the air for fourteen days that their 

 C02-content might come into equilibrium with the air, and then the rates of 

 bubbling of Elodea were measured in them. It is obvious that during the initial 

 period here figured, which is all Angelstein records, the bubble rates, rising rapidly 

 as they do, do not measure the COj-content, but merely the building up of the 

 o.Kygen diffusion gradients in the solutions. 



Fig. 3. — " Initial CO2 diffusion effect " with Elodea set up in a low concentration of CO3. 



strong CO2 solutions before use ; for the sodium bicarbonate solutions the 

 solid salt was dissolved directly in it. The test of its efficiency was that 

 when bubbling was started no such initial oxygen diffusion effects as are here 

 described were to be observed. 



Bb. Garhon Dioxide in Solution : the " Initial CO2 Diffusion Effect." — We 

 have now to deal with a second aberration depending on diffusion that 

 characterises the initial stages of bubbling in a solution. When a plant is 

 first put to bubble in a solution containing CO2 the layers against the plant 

 are charged with this solute to the same extent as the general body of the 

 fluid. As photosynthesis proceeds they are robbed of CO2 and a diffusion 

 gradient is gradually built up, supplying fresh CO2 from the more remote 

 layers. The effective concentration, then, is never so great again as at the first 

 moment. If the CO2 concentration is not very great compared with the 



