i 4 4 TRANSPIRATION AND ASCENT OF SAP ch. 



between the ends, which were ground flat, and the cylinder, 

 to make the joints air-tight. The lower end was per- 

 forated centrally, and in the perforation was sealed 

 hermetically a narrow brass tube, about 0*5 cm. in diameter, 

 projecting into the cylinder. This tube included the stem 

 of the plant to be experimented with, the lower end of the 

 stem projecting out of the cylinder while the leaves were 

 enclosed. To make an air-tight connection between the 

 tube and the stem, a stout rubber tube was first bound 

 on to the upper end of the brass tube. The branch was 

 then inserted into the rubber tube, and, before it had 

 been completely pushed down, a portion of it just above 

 the rubber was coated with thick glue, so that when it 

 was shoved down into its final position with reference to 

 the tube, it carried this glue down into the rubber tube. 

 When it was in position, a copper wire was bound tightly 

 round the rubber, and drew it into close contact with the 

 glue. To complete the joint, a little glue was smeared over it. 



The upper end of the cylinder was also perforated cen- 

 trally to admit the gas coming from the pump or bottle. This 

 was a simple screw-joint, made tight by a leather- washer. 

 To the upper end, and on the inside, were also attached 

 three hooks, from which were suspended a wire basket, 

 carrying drying materials, and a manometer. The latter 

 consisted of a simple, straight glass-tube, closed at one 

 end ; the other end dipped into a small vessel containing 

 mercury. This tube was marked off with J, J, J, i, etc., 

 of its length from its closed end, and the position of the 

 mercury index gave the pressures directly in atmospheres. 

 When the upper end of the glass cylinder was in position, 

 the drying materials and manometer hung in the cylinder. 

 The connection between the glass cylinder and pump or 

 bottle of carbon dioxide was made by means of a flexible 

 lead tube with screw couplings. 



Observations with compressed carbon dioxide. 

 When making these observations I was unable to procure, by 



