i 3 4 TRANSPIRATION AND ASCENT OF SAP ch. 



agrees well with the results obtained with the other 

 method. 



Method of eliminating surface clogging. In 

 order to determine the amount of flow without danger 

 from the error of clogging at the surface of supply, 

 it was measured in a lateral branch springing from 

 a stout stem. Water under pressure was supplied at the 

 two cut ends of the stem. With this arrangement, owing 

 to the relatively large surfaces of supply, the clogging 

 taking place at these does not encroach upon the amount 

 necessary for the supply of the small lateral branch for 

 several hours, and consequently the rate of transmission 

 in the lateral branch remains constant for this period. 

 To quote one of these experiments : A piece of yew stem 

 7*3 cm. long, having a straight lateral branch about its 

 middle, was selected. The diameter of the stem was 

 0*85 cm. and 105 cm. at each end respectively. Its wood 

 was also laid bare by an oval scar where another lateral 

 branch was removed. This scar was 1*3 cm. by IT cm. 

 The small lateral branch was cut to a length of 10*5 cm., 

 and its wood had a diameter of 0*47 cm. Not more than 

 a quarter of its cross-section was in a state suitable for 

 transmitting water the greater part being occupied by 

 blackened duramen. This lateral branch was fixed water- 

 tight in a rubber bung in an orifice in the bottom of a 

 tank in such a manner that the cut end of the lateral 

 branch projected from the tank, while the supporting stem 

 was immersed in the water in the tank. With the head 

 of 30 cm. 0-300 gramme was transmitted per hour. 

 The transmitting cross-section was about 0'043 sq. cm. 

 One-quarter of this area would be lumen : therefore 

 the velocity of flow must have been 27*2 cm. per hour. 

 If we reduce this to unit head the velocity becomes 

 about equal to 9*4 cm. per hour, which again falls 

 within the limits of the results obtained by the previous 

 method. 



