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



the dissolved salt. There is no support for Angelstein's view that such 

 plants actively decompose bicarbonates. 



Summary and Conclusions. 



Part I. — A glass " bubbler " has been devised which, fitted on to the cut 

 stem of submerged water plants, secures that the bubbles liberated in 

 assimilation are of constant size, thereby doing away with one of the chief 

 sources of trouble with this procedure. When, in addition, this bubbler 

 delivers bubbles into an isolated " bubbling cup " of distilled water, the 

 bubbles are removed from the direct influence of the solutions that are being 

 experimented with (see fig. 1, p. 307). In this way alterations of surface- 

 tension by added solutes are eliminated, and any osmotic effects on the cells 

 of the cut surface do not change the size of the bubbles. 



The disturbances of bubbling rate due to the " initial oxygen diffusion 

 effect " and the " initial CO2 diffusion effect " are explained and illustrated. 

 The former (see fig. 2, p. 310), due to inadequate oxygen content of the 

 solution, is of widespread occurrence with other workers, but is eliminated 

 in tliis work by using water heavily charged with oxygen. The CO2 effect is 

 the cause of the phenomenon of initial high bubbling rates which rapidly 

 decline (see fig. 3, p. 310). It marks the initial stage before a steady static 

 diffusion gradient of CO2 is set up. This effect cannot be eliminated when 

 CO2 is a limiting factor, but does not appear if light intensity is limiting. 

 As these two initial diffusion phenomena are independent and of opposite 

 effect, they may in some cases mask one another mutually, and give a record 

 which does not reveal the initial disturbances. 



Part II. Action of Acids upon Assimilation hy Submerged Water Plants. — 

 It is shown that the augmentation of bubble rate which Treboux has recorded 

 on adding acid is due to the acid setting free CO2, locally, from calcium 

 carbonate incorporated in the surface of plants growing in chalky waters. No 

 such acid effect is shown by the same plants when grown in soft water. 



That the action of the acid is merely to set free an additional supply of 

 CO2 is proved by the fact that, with plants grown in hard waters, acid only 

 produces an increase of bubble rate when CO2 supply is the limiting factor to 

 the rate of bubbling at the time the acid is added. If the plant is placed in 

 relatively strong CO2 and weak light, so that light is limiting, the addition of 

 acid has no effect upon the rate of bubbling. This evidence seems to dispose 

 of the suggestion that increased bubbling rate with acid is due to CO2 

 liberated from the adsorbed state and escaping as a CO2 addition to the 

 volume of the bubbles. This type of effect should not disappear when light 

 is limiting. 



