The Cause of the Excretion of "Water on the Surface of Nectaries. 9 



water-pore where it finds the least resistance. Such excretion can only 

 take place when the whole mass of plant lissue is in a State of turgescence. 

 On the other liand the excretion of water by the nectary depends upon 

 the osniotic action of a fluid on its surface. Whether this fluid on the sur- 

 face of the nectary has more or less osmotic power Ihan the conlents of the 

 cells acted upon, or whetlier the cells are wholly or only in a partial State 

 of turgescence will eff'ect the excretion only in its rapidily. The required 

 conditions for this one-sided water current exist when the cells are filled 

 with a Solution capable of generaling more or less pressure, and their outer 

 walls are penetrated with a fluid of a diflerent quality from that permeating 

 the inner and opposite walls. 



The monient the entire wall of any given cell becomes saturated with 

 a fluid of like quality, that moment all one-sided water flowing slops so far 

 as caused by its own activily. 



Neither the concentration of the nectar on the surface of the cells, nor 

 that of the fluids filling the same, can ofler any rules with reference 

 to the excretion, unless we take into accounl the pernieability of the cell- 

 walls and the fluids which Surround them. 



Relation of Pressure to the Excretion of Nectar. 



The excretion of water on the margins, teeth and tips of leaves of 

 many plants, can at any time be reproduced by placing the given plants, 

 after having cut them from the parent stem, under pressure i). 



The excretion of the nectar cannot be reproduced in this way. Many 

 nectaries on a brauch of Prunus laurocerasus, which had been washed 

 until they remained dry, were subjected to a pressure of a column of mer- 

 cury 4.5 Ctm. in height. They remained under this pressure 24 hours, 

 covered with a bell-jar, and in a saturated atmosphere without showing 

 any moisture on their surfaces. 



The water was forced into the leaves injecting the intercellular Spaces, 

 and flowing out in drops on wounded places. I have repeated this experi- 

 ment on several plants. The result has been always the same, even with 

 Acer pseudoplatanus, where the nectar finds its way to the surface 

 through stomata. These stomata open however into a single wide space 

 which has no connection whatever with the intercellular Spaces of the leaf. 

 It is readily seen from the above that water filtrates with little or no read- 



1) Ttie appearance of small drops of water on the tips and teeth of the leaves of many 

 plants in a moist atmosphere is by no means wholly due to the so called root-pressure. 

 The tissues of the stem may share in producing this effect. By taking thrifty plants of 

 Impatiens glandulifera and culting the stems off under water, and then placing the 

 severed plant under a bell-jar in a moist atmosphere, many small drops will appear on 

 the teeth of the leaves; occasionally large ones. This is also true with I. parviflora and 

 Fuchsia. — Mqll 1. c. 



