1883.] Significance of Water Glands and Nectaries. 47 



tissue. The nectary tissue may or may not be supplied with 

 vascular bundles, and may or may not be provided with stomata. 



As with water-glands, so with nectaries, the investigations 

 extant, deal mainly with histological details ; and with the excep- 

 tion of the observations of Sachs 1 and Wilson 2 , the physiological 

 significance of these structures has only been treated of generally, 

 and has received but little special attention. 



Sachs pointed out that the secretion of nectar was independent 

 of root-pressure, and states that the exudation of this liquid was 

 due to the activity of the nectary cells themselves. Wilson, on 

 the other hand, maintains that it is due to osmosis, and not to 

 internal pressure. 



Dealing first of all with Wilson's view, it may be stated that 

 he comes to his conclusions chiefly from the fact, that a passage of 

 fluid from the cells of a tissue to the exterior, may be induced by 

 placing on the surface any substance or liquid which causes 

 osmosis, e. g. a drop of gum solution on a leaf of Buxus sempervi- 

 rens : that the secretion is wholly under the control of external 

 manipulation, for it may be stopped by repeatedly washing the 

 nectary, and drying with blotting-paper, or induced again by the 

 application of sugar or sugar solution : and that much collateral 

 evidence is afforded by the consideration of what takes place in 

 such structures as the glands of Dionaea which require the 

 stimulus of some nitrogenous substance before the secretion of the 

 digestive fluid takes place. He also draws attention to the fact 

 that in nectaries we find that the most external walls of the 

 nectary cells undergo a mucilaginous degeneration, and it is the 

 mucilage thus formed, which by its osmotic properties starts the 

 flow of nectar in the first instance. Subsequently, the flow is 

 maintained by the osmotic activity of the nectar secreted, which is 

 materially concentrated in consequence of gradual evaporation. 



One cannot, I think, accept in their entirety Dr Wilson's views 

 for several reasons. We have to begin with so many instances of 

 a well-defined secretion on the part of vegetable cells, that we 

 should expect on many grounds that the secretion of nectar was 

 due to the activity of the constituent cells ; but placing aside such 

 considerations, one must turn especially to Dr Wilson's experiments 

 and deductions. 



It is a fact that the external walls of certain nectaries, e.g. 

 those of Nigella and Oestrum, so well figured by Behrens 3 , do 

 undergo mucilaginous degeneration, but so far as I know, this 

 cannot be taken as the universal rule, but as one is inclined to 



1 Sachs, loe. cit. 



8 Wilson, "The excretion of water from the surface of nectaries." Unter. Bot. 

 Institut, Tubingen, 1881. 



3 Behrens, loc. cit. See Tab. II. Figs. 5, 6, 9 and 10. 



