i THE NATURE OF TRANSPIRATION 21 



the saturated chamber. For this purpose I used the leaves 

 of Eucalyptus globulus, and found that their apical veins 

 were injected often after standing only 30 min. in eosin, 

 when surrounded with a saturated atmosphere. The eosin, 

 to do this, had risen 20 cm. in the leaf above the level of 

 the solution in which the leaf stood. In this case it is 

 evident that the cells of the leaf must have been solely 

 responsible for the observed elevation. 



But the directed pumping actions which cause the eleva- 

 tion of the coloured fluid in these cases, although mostly 

 confined to the leaf, do not appear to be restricted to any 

 special cells forming water-glands on the surface of the 

 leaf. It seems most probable that most or all of the cells 

 bordering on the vascular capillaries, both in leaf and 

 stem, are able to exert a tractional force on the water in 

 the conduits, and are able to expel water, when thus drawn 

 in, on their outer surfaces. It may be, however, that the 

 cells of the water-glands of plants are more highly special- 

 ised for this function, and hence the exudation of drops 

 on leaves of plants in a moist atmosphere takes place over 

 these glands or hydathodes, as Haberlandt prefers to call 

 them. 



The following observation shows that the elevation of 

 the water is not solely due to the functioning of these 

 water-glands, even in plants possessed of these structures. 

 The leaves of Escallonia macrantha, Chrysanthemum sinense, 

 and Chrysanthemum lacustre have water stomata on the 

 margin of the leaf ; but if these glands are removed by 

 cutting away the whole margin with a scissors, it will be 

 found that water will be drawn up into these leaves through 

 the stem almost as quickly as into leaves which are left 

 intact. 



Another observation which shows that the traction is 

 exerted by cells of the leaf, which are not visibly differ- 

 entiated, may be made on Cheiranthus cheiri. The leaves 

 of this plant, so far as I can make out, have no specialised 



