able secretion of water: a full-grown leaf secreted during 

 one night 2.76 g. of water (that is 26 per cent, of its own 

 weight.) Through this peculiarity the water supply within 

 the plant is regulated and the danger avoided that any water 

 should penetrate the surrounding tissue in consequence of 

 strong root-pressure, — which would naturally obstruct the 

 vital function of the entire leaf. Besides it is to be noticed 

 that in this way an abundant flow of water is produced : the 

 plant takes up large quantities of water from the earth, 

 laden with nutritive salts, and the distilled water is almost 

 pure (it contains only 0.045 g. salts), so that the nutritive 

 salts are absorbed by the plant. 



From these considerations it necessarily appears that 

 the hydathodes are of great biological importance to the 

 plant. 



Haberlandt then "poisoned" the plant, by sprinkling 

 it with a o.i per cent sublimate solution of alcohol. The 

 purpose of this experiment was to ascertain whether in 

 the secretion of water there was question of a merely phys- 

 ical process or of a vital process. In the first case the 

 action of the hydathode should continue even after the 

 treatment with the sublimate solution, while in the latter 

 case it should not. As the secretion ceased the obvious 

 conclusion to be deduced from this experiment is that the 

 hydathodes do not act as purely mechanical filtration-ap- 

 paratuses, as one might have thought, but that there is 

 here evidence of an active vital process in the plant; the 

 unusual term "poisoning" is therefore really justified under 

 present circumstances. 



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