BY ALEX. G. HAMILTON. 765 



that the absence of cavities in some species is a by no means 

 uncommon occurrence, and Lundstrom and Lagerheim note the 

 same fact. 



The upper surface of the leaf is extremely glossy and dark 

 green ; the under side is duller and lighter in colour. When 

 dipped in water, the upper wets readily, while the water gathers 

 in patches on the under side, as if it were greasy. The pits appear 

 on the upper surface as very distinct, though small, domed pro- 

 tuberances, circular or elliptical in outline (fig. 3); they are flatter 

 on the under side (tig. 2). They vary in size in mature leaves 

 from 1 to 3-5 mm. in diameter (outside measurement), and the 

 depth is usually two-thirds of the diameter. The opening is 

 small and usually circular, and in the largest about -75 mm.; it is 

 surrounded by a thickened rim in which are vascular bundles 

 proceeding from the veins between which it occurs; the rim is 

 lighter-coloured than the rest of the leaf. The interior is usually 

 lined with 1 -celled hairs. Stomates occur plentifully on the lower 

 side of the leaf, but they are absent in the domatia and on the 

 upper side of the leaf. The pits are often inhabited by minute 

 Acari, and their ova and excrement are also found in them. The 

 mites sometimes quit the cavities and wander about on the under 

 surface of the leaf. I have also seen similar Acari in the 

 stomatal cavities of Banksi'i, in the rolled leaves of Ricinocarpus, 

 (fee, and in any other cracks or cavities suitable for shelter in 

 plants. 



The microscopic examination of sections of the domatia cut at 

 right angles to the midrib and vertically, as regards the blade of 

 the leaf, shows the structure described below, which is pretty 

 constant in all the domatia I have cut. Beginning at the upper 

 surface of the leaf, i.e., on the upper leaf -surf ace there ai'e — 



(1) The cuticle, which is thin (fig. 5a). 



(2) An epidermis composed of one layer of small oblong cells 

 (fig. 56). 



(3) A single layer of hypodermal cells (pe) much larger than 

 those of the epidermis, and from elliptical to oblong in shape, with 

 thickening at the angles. These cells are veiy thick-walled, and 



