70S DOMATIA IN CERTAIN AUSTRALIAN AND OTHER PLANTS, 



alternately. They vary in number from 3-8. They rarely occur 

 in the forks of the secondary veins. The leaf is very dark green, 

 and has a varnished upper surface; it is lighter in colour and 

 duller below. It wets readily on the upper side, but is greasy on 

 tlic under side. It is very thick, fleshy and soft, and the rim of the 

 cavities does not project beyond the veins as in Pennantia. They 

 show above as slight rounded projections and have a round orifice 

 below, surrounded by a slightly thickened rim, the thickening 

 being internal. Internally they are lenticular, 2-3 mm. in external 

 diameter and the opening -S-l mm. The interior cavity is pro- 

 portionately smaller than in Pennantia. The rim is lighter in 

 colour than the rest of the under surface. The interior is lined 

 with thick-walled unicellular hairs (fig. 11), and hairs of the same 

 kind occur on the midrib below, sparsely on its upper surface, and 

 veiy plentifully in the channel of the petiole in young leaves. A 

 section of the cavity perpendicular to the plane of the leaf and 

 across the axis of the cavity shows the following structure, 

 beginning on the roof — the upper surface of the leaf : — • 



(1) The cuticle. 



(2) The epidermis, composed of one layer of small elliptical or 

 oblong thick-walled cells. 



(3) A single hypodermal layer of oblong cells with thickened 

 walls, and almost always without protoplasmic contents. 



(4) The palisade-parenchyma, made up of four or five rows of 

 oblong cells little longer than wide, and very rich in chromato- 

 phores, sometimes as many as 20 lining a single cell. Besides 

 these, there is often a highly refractive globule, yellowish-green 

 in colour, and like an oil drop, which dissolves in ether and is 

 probably a resin or oil. The cells of the highest row are much 

 larger than those of the lower ones, each succeeding layer being 

 of smaller cells. The outer cells are here and there empty, and 

 occasionally a whole row is in this state, and then, except for the 

 vertical position, they resemble the hypodermal layer, and as in 

 Pennantia the latter appears to be derived from them. Under 

 this lies : — 



