Greensill. — Leaf-structure of Coprosma. 353 



carptts, in the stornatal crypts of Banksia, and other cracks 

 and cavities suitable for shelter), their occasional presence in 

 the pits may be accounted for by the fact of these pits present- 

 ing a suitable place for shelter. Therefore I incline to think 

 that there is no connection between the formation of the pits 

 and the visits of the insects. 



Mr. Hamilton also in his paper discusses and dismisses 

 the probability of the pits being pathological in nature ; being 

 glands ; being cavities for sheltering stomata ; or being extra 

 growths caused by the superabundance of sap. As these sup- 

 positions have been sufficiently discussed, I will merely notice 

 in passing the following facts in reference to them : There was 

 no sign of any diseased condition of the leaf-tissues, except in 

 the case already mentioned ; there was no sign of any secre- 

 tion from the hairs or epidermal cells of the pits ; there were 

 no stomata in any of the pits. Mr. Hamilton mentions, 

 finally, the possibility of these pits being organs for the 

 absorption of water or vapour, and dismisses this theory also 

 owing to his inability to fill the pits with water. I tried first to 

 fill the pits with an alcoholic stain, as did Mr. Hamilton, 

 and succeeded without any difficulty. The epidermal cells 

 and hairs of the pit in a few minutes showed a faint tinge of 

 the colour of the staining material in their cells. But, lest 

 the alcohol should affect the absorbing-capacity of the living 

 cells in any way, I tried covering the surface of the leaf with 

 water in which was mixed finely powdered carmine. After 

 leaving it for a short time on the surface of the leaf I washed 

 off all traces of the carmine, so that in the action of cutting I 

 might not introduce any of it into the pits. I then cut sections 

 through the pits, and found that there were numerous grains 

 of carmine adhering to the cells of the epidermis and hairs of 

 the pit. The hairs may serve especially to suck up water, 

 though the epidermis probably aids in the process, for in 

 Goprosma linear if olia there are no hairs in the pits, and in 

 some other species they are not numerous enough to be of 

 themselves of great importance. The presence of a cuticle 

 outside the epidermal cells and hairs need be no hindrance to 

 the theory of the pits as absorbing organs, for it is not often 

 thick. A cuticle, unless very thick, is not impermeable to 

 water ; and even when very thick it is not so much its thick- 

 ness that prevents the absorption of water through it, but the 

 presence of and amount of wax in the cuticle, and the 

 contents of the cells it covers. As to the contents of the 

 cells, I can say nothing for certain. I could see in the hairs, 

 in the cells of the colourless layers, and the epidermis of the 

 pit, minute or larger round bodies, some of which may 

 have been drops. They were clear and transparent look- 

 ing. I could also see these in the cells of the hypo- 

 23 



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