Dixon — Vitality and Transmission of Water through Plants. 27 



of the branch during the steaming might just compensate for their removal. 

 The possibility of such a coincidence, though very improbable, suggested the 

 use of picric acid as a killing agent in place of steam. 



The experiment was at first arranged in just the same manner as before; 

 and the initial rates of transmission of the experimental and control branches 

 were determined. Then some dry picric acid was introduced into the water- 

 tube of the experimental branch, and the observations were continued. No 

 change could be detected in the rates of transmission which could be assigned 

 to the removal of vital actions by the picric acid, even when the latter appeared 

 at the lower end of the experimental branch. 



The gradual killing of the braucli and the slow penetration of the picric 

 acid in this method are open to objection, and would tend to render a oliange 

 due to death less noticeable. To remove this objection, a modification was 

 introduced by means of which the picric acid is quickly forced through the 

 stem under pressure ; and, in order to place the control under similar con- 

 ditions, distilled water is simultaneously forced through it. This is arranged 

 by liaving the tubes containing the water-supplies to each branch provided 

 with a side-tubulure connected with a J -shaped glass tube containing a 

 mercurial column. The J -tubes and the tops of the water-supply tubes are 

 provided with stop-cocks (e,/, ^, and Ii respectively, fig. 1, p. 23). At first the 

 side-tubulures {e and/) are closed ; and the rate of transmission of distilled 

 water under a low pressure is measured for each branch ; then picric acid is 

 introduced into the supply-tube of the experimental branch, and tlie stop- 

 cocks at the upper ends of tlie supply-tubes {g and h) of both are closed, 

 and the lateral tubulures (e and /) opened ; so that the picric acid is forced 

 through one, and distilled water is forced through the other. When the 

 picric acid appears below, by the suitable manipulation of tlie stop-cocks, the 

 pressure in each is again reduced, a.ud observations are recommenced. 



Table II. gives the figures of such an experiment, and tlie results are 

 plotted graphically in fig. 3. 



Particularn of Expeyimeiit. 



A and B, two similar branches of Syriiuja vulgaris : A with seven year- 

 rings ; length, 80 cm. Upper diam. of wood, 085 cm.; of pith, 0'14 cm. 

 Lower diam. of wood, 0*92 cm. ; of pith, 0*20 cm. Head, 24 cm. of water. 

 B witli 4 year-rings ; length, 80'O cm. Upper diam. of wood, 0'85 era. ; of 



