314 Mr. A. J. Wilmott. Ex2Derimental Researches on 



Part II. — Assimilation by Elodea in Dilute Solutions of Hydro- 

 chloric Acid. 



Treboux (1903) tried the effects of many solutes upon the rate of bubbhng 

 of submerged plants, and he found that they all had a depressant effect, 

 except one class of substances — the organic and inorganic acids — which 

 increased the bubbling rate considerably. Treboux does not seem to have 

 considered this at all an amazing result, but simply analogises these acids 

 with carbonic acid, which, of course, also produces the same consequence. 

 At the suggestion of Dr. Blackman, I took up this problem to test whether 

 this general action of acids is due to any direct action on the cell, or merely 

 to their setting free carbonic acid from the plant, and ' so leading to an 

 increased assimilation. Hydrochloric acid was selected for experiment, and 

 it soon became clear that its action is of the indirect nature here suggested. 

 All this work was done in 1911. The only modern comment on Treboux's 

 results that has been noted is by Willstatter (1918, pp. 53-4), who thinks it 

 improbable that they are due to a direct action on the photosyuthetic 

 mechanism. He suggests that it is more probable that the acid acts on the 

 COg-adsorbing property of living tissues, an effect which he has studied, 

 displacing CO2, which may increase the bubbling, partly by escaping as a 

 constituent of them, and partly by augmenting assimilation. 



Treboux's observations with acids were numerous, and his effect is 

 perfectly well established, though he notes that some other observers have 

 failed to detect it. A single example will illustrate his results (Treboux, 

 Experiment 36). The bubble rate was observed in water containing 0"3 per 

 cent. CO2, and then increasing quantities of acid were added, the increase of 

 bubble rate being recorded for each stage : finally, the plant was returned to 

 CO2 solution without acid. The solutions and rates are as follows : — 



Concentration HCl in addition 



Nil 



-0001 N • -0002 N 



-0003 N 



-0004 lif 



Nil 



to 0'3 per cent. CO2 















26 



46 66 



1 



86 



106 



26 



Were Elodea one of those water plants which become in time obviously 

 encrusted with chalk, explanation of the action of acids would be simple, but 

 to the eye there is no sign of such incrustation. 



Experimental Results. 



Experiments were first made in spring with Elodea that had been growing 

 all the winter in an open wooden tub, the water in which was largely rain 

 water. 



