22 Shirley and Lambert : 



are three to four cells thick, the elements unequal in size, and arranged 

 in oblique series. The cells are evidently of two types, the outer ones 

 showing circular bordered pits, which in the inner cells are absent. 



4. The Functions of the Pits. 



My colleague, C.A.L., examined a large number of leaves in Mel- 

 bourne gardens, and in no case found insect guests inhabiting the 

 pits; an examination of plants in the Sydney Botanic Gardens in. 

 January, 1921, and in the Brisbane Botanic Gardens in October, 1921,. 

 also gave negative results. Miss Greensill reports similarly of her 

 experience of New Zealand species of Coprosma. This seems to dis- 

 pose of Lundstrom's theory that the pits are the homes of commensals. 

 To test whether these pores are sources of a supply of moisture to 

 the leaf, similar to those figured by Kerner and Oliver (12) the pits 

 on healthy leaves, still attached to the plant, were filled by C.A.L, 

 with a quickly drying varnish, and flourished as well as ever, prov- 

 ing that absorption through the pores is no necessary function. It 

 has already been stated that the pits do not contain stomata, and 

 that these organs are minute in size, and numerously spread over the 

 surface of the lower epidermis. After exhausting the aids of the 

 microscope and of experiment, our conclusion is that the pores were 

 formerly of assistance to the plant when under xerophytic conditions,, 

 and that in the Miocene age of continental New Zealand, the stomata 

 were confined to them, as in the leaves of many of our Hakeas, but 

 that with modern and more humid conditions, the leaves have 

 developed stomata on their lower epidermis, and the pits are now 

 useless to the plant, having only an interest to the teleologist. 



EXPLANATION OF PLATE IV. 



Fig. 1 — Transverse section of leaf. 



e. Pit. 



f. Midrib. 



Fig. 2 — a. Epidermis and cutin. 



b. Epidermal cells of second layer. 



c. Palisade cells. 



Fig. 3 — Epidermis, underside of leaf. 

 Fig. 4 — Upper epidermis, surface. 

 Fig. 5 — Transverse section of young twig. 

 Fig. 6 — Tangential section. 



a. Medullary rays. 



b. Fibre tracheids. 



c. Trachea. 



Fig. 7 — Basal membrane of pit. 



Fig. 8 — Nucleated hair from base of pit. 



BIBLIOGRAPHY. 



1. Cheeseman, T. F. — Manual of the New Zealand Flora, 1906, p. 243. 



2. Bentham— Flora Australiensis, Vol. III., pp. 429-30. 



