76 TRANSPIRATION AND ASCENT OF SAP ch. 



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, f, g, and h respectively, Fig. 13, p. 70). At first the 

 side-tubulures (e and /) are closed ; and the rate of trans- 

 mission 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 the stop- 

 cocks at the upper ends of the 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 the stop- 

 cocks, the pressure in each is again reduced, and observa- 

 tions are recommenced. 



Tables 8 and 9 give the figures of such an experiment, 

 and the results are plotted graphically in Fig. 15. 



Particulars of Experiment. 



A and B, two similar branches of Syringa vulgaris : A 

 with seven year-rings ; length, 80 cm. Upper diam. of 

 wood, 0'85 cm. ; of pith, 014 cm. Lower diam. of wood, 

 - 92 cm. ; of pith, 0*20 cm. Head, 24 cm. of water. B 

 with four year-rings ; length, 80'5 cm. Upper diam. of 

 wood, 0*85 cm. ; of pith, 0'16 cm. Lower diam. of wood, 

 0*95 cm. ; of pith, 0'20 cm. Head, 24 cm. of water. 



Table 8. 



