338 s. KUSANO : transpikation of 



fresh cut-branches/^ Moreover in the case of cut-branches we 

 meet with the existence of negative pressure, which may some- 

 times produce great errors in the measurement of transpiration. 

 Certain plants, for instance, Daphniphyllum macropodum, 

 when cut off at 12. ,50 \).m. and observed at 1 p.m. and in each 

 succeeding interval of 10 minutes, the following lengths of the 

 column of water in the capillary tube were found to have been 

 absorbed, under a constant temperature : — 



226, 144, 120, 106, 102, 103, 89, 89, 88, 89, 88, 87, 

 85, 85, 82, 79, 79, 78, 79, 79, and so forth. 

 In Pasania ciispidata taken at 8.50 a.m., I observed at 9 a.m. and 

 every succeeding 10 minutes, as follows : — 



47, 38, 31.5, 28.5, 26, 23.5, 23.5, 22, 22, 22, 

 21, 20.5, 20, 19.5, 18, 19, 20, and so on. 



The greater amount of absorption at the beginning of the 

 experiments shows that the water is taken up by the plant in 

 consequence of the existence of negative pressure, rather than 

 merely to supply the loss of water effected by transpiration at 

 that time. 



To avoid, as much as possible, such disturbing conditions, 

 the experiments were carried on in a room where the temperature 

 and humidity were kept nearly constant ; and the experiments 

 were commenced two hours after the cut-branches had been 

 placed in the room, when the negative pressure had nearly 

 ceased and at the same time the branches had become somewhat 

 accustomed to the conditions in the room. With regard to the 

 preparation of the branch, a part of the required plant, the 



1) A gradual diminution of absorption of water by cut-branches has been pointed out 

 by Sachs (Flora, 1856). F. Darwin and W. Phillips have noted the precautions 

 to be observed while using the potometer in their paper " On the Transpiration-Stream in 

 Cut-Branclies " (Proceed, of the Cambridge Philos. Society, Vol. V, Pt. V, 1885, p. 330). 



