Vegetable Assimilation and Respiration. 307 



That this effect really exists was demonstrated by some special experiments 

 in which air was forced slowly by pressure through a short length of Elodea 

 stem (one or two internodes), so that it escaped in bubbles at the free end. 

 The other end was connected by rubber and glass tubing to a head of water 

 forcing air through the plant.' A scale was placed behind one of the inter- 

 vening tubes, and the travel of the air-water meniscus at the head of the 





























3>-: 



1 



1 













Fig. 1. — Fig. 1 shows the arrangement of the parts during experiments. A, flat-sided 

 glass museum jar, containing the experimental solution ; B, "bubbling cup," con- 

 taining distilled water, closed by cork below ; C, wax mixture, which supports the 

 shoot in the cork and completely separates the liquids in A and B ; D, cork lid, 

 which hinders the loss of CO2 from the top of the solution and supports the 

 bubbling cup and also a thermometer. The glass " bubbler " is shown attached 

 to the cut end of the shoot with a bubble escaping from it. [In the figure, to save 

 space, the shoot and the jar, A, are drawn much too small and short relatively to the 

 essential central parts.] 



column of water was read for a given number of bubbles. When the index 

 column of water had reached the end of the scale, the connection was inter- 

 rupted and the index sucked back, so that further readings could be taken 

 after re-connecting. The whole was so arranged that the final glass tube 

 carrying the Elodea shoot, came up through a cork in the bottom of a vessel 

 into which various hquids could be introduced. 



VOL. XCTI. — B. 2 A 



