632 Proceedings of the Royal Irish Academy. 



Impatiens, Fuchsia, Limoniastrum, and Polypodium, if cut branches of 

 these plants are set in ^^ater in a moist place. His results have been 

 confirmed by Haberlandt^ and JNestler,^ though curiously enough the 

 last-named author attributes the di-opping to a filtration of water 

 through the water-gland due to the pressure from behind. Haber- 

 landt and Pfeffer,^ however, are agreed that the expulsion of the 

 water is due to the vital activity of the cells of the gland. In the 

 experiments alluded to there seems no probability of any pressure exist- 

 ing in the water in the conduits tending to exptl water from them. 



It was usually found at the end of all the experiments conducted 

 in the saturated chamber that the surfaces of the leaves had a copious 

 deposit of water upon them, and so it seemed probable that water was 

 actually extruded from the cells of the leaf even after water had begun 

 to condense on them from the surroundings. 



The actual presence of free liquid on the surface of the leaves 

 apparently did not markedly diminish the rate of rise of the coloured 

 fluid in the branch, and so, if the branch was immersed in water before 

 commencing the experiment, it was found that the eosin mounted not- 

 withstanding into the di'ipping leaves. 



In these cases, the j)umping cells, being surrounded by water, must 

 possess a directed action, drawing the water in on one side from a 

 liquid supply, and expelling it on the other into free liquid. 



This directed action may be more strikingly demonstrated by the 

 following experiment : — A branch is fixed water-tight into the lower 

 narrow opening of a glass receiver, so that its upper part and leaves 

 project into the receiver, while its base extends beyond the cork in 

 the neck, and is supplied with a solution of eosin (see fig. 2). If the 

 receiver be filled with water, so that the leaves of the branch are 

 completely submerged, it will be found that, notwithstanding the 

 presence of the water in contact with the leaves, and the hydrostatic 

 pressure due to its depth, the eosin will mount rapidly into the 

 branch. 



In some of my experiments the pressure of the water was sufficient 

 to dii^e liquid back into the intercellular spaces of the leaves of the 

 branch. So that it appears that the pumping action can raise water 

 against a considerable external hydrostatic pressure. 



1 Sitzb. d. k. Akad. d. Wissenschaft in Wien. Bd. ciii. 

 ^ Ibid., Bd. cv. 



^ Pflanzenphysiol. Bd. i. 174, and Haberlandt, Jahrb. fur wissenscliaftliche 

 Botanik, 1897. 



