50 



Prof. H. H. Dixon. 

 Table III. 



[Nov. 7, 



Length of piece. 



Head. 



Distance traversed. 



Time. 



Velocity per hour 

 per unit head. 



centimetres. 

 8 

 6 

 6 

 6 

 6 



centimetres. 

 2 

 2 

 3 

 3 

 3 



centimetres. 

 0-7 

 0-8 

 1-8 

 0-9 

 0-7 



minutes. 

 20 

 20 

 15 

 15 

 15 



centimetres. 

 8-4 

 7-2 

 14-4 

 7 2 

 5-6 



as the velocity under a head equal in length to the stem. The last 

 observation of the series was made on a piece of a narrow branch about 

 0*5 cm. in diameter, the others on pieces about 1 cm. in diameter. This 

 difference appeared almost constantly in my experiments. The thin distal 

 portions of the wood in almost every case offer a greater resistance to flow 

 than the thicker parts. The high estimates of resistance are almost always 

 obtained with the former. This fact is probably of importance in 

 determining the total resistance in the intact plant. I have included 

 the third observation in the table, although it diverges so markedly from the 

 mean, because I could see no error in the experiment, and it is quite possible 

 that a maximal result like this is the nearest to the actual flow in the 

 uninjured tree. 



The higher mean in the second series of experiments for the velocity of 

 transmission is probably due to the fact that clogging substances are less 

 likely to accumulate owing to the actually slower flow and to the position 

 of the surface of application. 



With care, good results may be obtained with higher pressures, if the 

 supply is from below. In the following experiments (Table IY) the cylinder 

 of wood was fixed in the short arm of a vertical J -tube filled with a repeatedly 

 filtered solution of ferrocyanide of potassium. The moment of penetration 

 through the wood, which was 3 cm. long in each case, was determined by its 

 reaction with ferric chloride applied in a piece of bibulous paper to the upper 

 surface of the cylinder. 



The mean of the entire series gives 6*9 cm. per hour as the velocity at 

 unit head. As all the known errors, such as the introduction of bubbles, 

 clogging and injury of the tracheidal tubes, tend to reduce the result, it is 

 probable that the velocity in the intact tree would be at least 7 to 8 cm. 

 per hour under the same pressure. The occasional high results obtained 

 indicate a still higher figure as the probable velocity. 



In fig. 2 I have plotted these results. The ordinates represent the length 



