138 Gibson. — Contributions towards a Knowledge of 
22 . S. plumosa, Bak. (Fig. 21.) 
Ventral leaf. Oblong pointed, spiny but non-sclerotic margins. 
Several stomata occur on the outside marginal region of the ligular 
face as well as over the midrib on the aligular face. 
Dorsal leaf. Broadly ovate and suddenly acuminate with spiny 
margins. No stomata occur on the ligular face. 
In section the leaf of the species approaches that of S. Wildenowii , 
the peg-shaped ligular epidermal cells being followed by a layer of 
small cells with large chloroplastids— a pseudo-palisade-layer — followed 
in turn by a reticulum of larger rounded cells, abutting on the aligular 
epidermis (Fig. 21). 
23 . S. Douglasii, Spr. (Fig. 1.) 
Ventral leaf. Ovate, oblique, bluntly pointed, with a few hairs on 
the basal lobes. The spines are commonly sheathed at the base by 
marginal leaf-cells. The margin is not sclerotic, but the cells are 
warty. Stomata occur on both faces, over the outside of the basal 
lobe on the ligular face, and over the midrib on the aligular face. 
The dorsal leaf is similar in shape with a cusp provided with 
hooked spines. The margin is similar to that of the ventral leaf. 
Stomata occur on both surfaces. 
In section the leaf shows a reticulate mesophyll only — there are no 
palisade-cells. 
Both of these species (22 and 23 ) show a tendency to have the ligular 
and aligular epidermis composed of somewhat similar cells, and thus 
form a transition to types B and C. 
The succeeding ten species conform in the structure of their leaves 
to the Martensii- type, although their stem-anatomy shows a distinct 
advance, having three or more steles instead of one. 
24 . S. inaequalifolia, Spr. 
Ventral leaf. Oblique awl-shaped, bluntly pointed, with sclerotic 
faintly spiny margins. The axillary leaf resembles the ventral, save 
that the lamina is equalized. Stomata occur on the aligular face 
plentifully, and a few also occur near the margin on the ligular face. 
Dorsal leaf. Similar in shape to the ventral leaf, but narrower. 
Stomata occur on the aligular face only. 
Section. Similar to that figured for S. Wildenowii (Figs. 30, 31). 
