EVERGREEN TREES IN WINTER. 337 



preferred here for ascertaining the amount of water transpired 

 from cut-branches. A consideration of the relation between 

 absorption and transpiration ought not to be neglected, when, as 

 in the present instance, we use this method. While the outer 

 conditions are constant, the relation between these functions 

 also remains the same, but any violent change in the former at 

 once modifies the latter ; as is shown by the experiments of many 

 investigators.^^ Eberdt"' has also shown that the excess of ab- 

 sorption occurs at night, while on the other hand, the excess of 

 transpiration is observed in the daytime as the obvious 

 result of the change of outer conditions, such as temperature and 

 humidity, to which the plant is exposed during both day and 

 night. To make the amounts of both absorption and trans- 

 piration approximately equal, the external conditions, which effect 

 these functions, must be kept constant, and in this case only 

 can the amount of absorption be regarded as an indication of the 

 amount of transpiration. 



A remarkable fact, not overlooked in my investigations, is 

 that the absorption by cut-branches behaves differently from that 

 of a rooted-plant. As the cut-branches are, strictly speaking, 

 dying parts of the plant, not only is their absorbing power 

 gradually weakened thereby, but also the filtrating activity of the 

 cut-surface of the branches sometimes becomes weaker in conse- 

 quence of the varying conditions to which they are subjected.'^^ 

 It is requisite, therefore, that the experiments should be made with 



1) Burgerstein, ]\Iaterialien. II, p. 55. 



2) Eberdt, Die Transpiration der Pflanzen und ihre Abhängigkeit von äusseren Be- 

 dingungen 1889. 



3) Pfeffer, Pflanzenphysiologie 1897, 2 Aufl. Bd. I, p. 209. 



