136 TRANSPIRATION AND ASCENT OF SAP ch. 



These results confirm the received view that the amount 

 transmitted varies directly with the pressure. The slight 

 bending over of the line joining the observations at the 

 high pressures is amply explained by the gradual clogging 

 which takes place despite all precautions ; for the experi- 

 ments giving these results were made with the same piece 

 of wood after those at lower pressures had been carried 

 out. 



Table 16. 



The proportionality of head to flow may be indirectly 

 investigated in another manner. A straight branch fixed 

 in a horizontal position is connected to a large vessel of 

 distilled water. Precautions are taken to clean the con- 

 nections and the freshly cut inner end of the branch. A 

 tongue of bibulous paper is applied to the outer end to 

 draw off the transmitted water. The head once adjusted 

 is kept constant ; but after each determination the branch 

 is shortened. Fig. 22 records such a series of experiments. 

 The head throughout these was 100 cm. The initial length 

 was 25 cm. At that length the flow was 1*18 mg. per 

 second. Five centimetres were then cut off the outer end 

 and the flow rose to T66 mg. per second. A shortening to 

 15 cm. increased the flow to 2 33 mg. When the branch was 

 10 cm. and 5 cm. long, the flow was 3*79 mg. and 6'70 mg. 

 respectively. The curve plotted in Fig. 22 is a rectangular 

 hyperbola in which M = K./1 ; M being the number of milli- 



