146 Gibson . — Contributions toivards a Knowledge of 
stomata occur on both ligular and aligular faces of both dorsal and 
ventral leaves. 
In section the leaf resembles A. helvetica (Fig. 23), but the cells of 
the reticulate mesophyll next the ligular face are more closely packed, 
forming a pseudo-palisade-layer. Distinct emergences occur on the 
basal lobes, consisting of three, four, or more thick-walled spines, fused 
together. 
48. S. pilifera, A. Br. 
The leaves of this species are very similar to those of S. involvens . 
The apices are long, and the margins are sclerotic and very spiny. 
Stomata occur on both ligular and aligular faces of both ventral and 
dorsal leaves. 
The leaf in section shows the same characters as that of the 
preceding species. 
The remaining three species belonging to this series differ 
from those already described in having spirally arranged 
similar leaves. In structure, however, they closely resemble 
those of the Galeottii- type. All three have strongly sclerotic 
leaf-cells of dense and firm texture. The leaves are further 
equal-sided and fringed with well-marked spines or emer- 
gences. The reticulate mesophyll is large in amount, and 
there is no palisade-layer. 
D. Spinosa-type. 
49. S. spinosa, A. B. (Fig. 26 .) 
The leaves of the erect vegetative axis are approximately similar. 
The first leaves on the creeping portion of the stem, which are often 
opposite or nearly so, are ovate acuminate and placed far apart. 
Their margins are entire, or have one or two multicellular spines. 
On the erect axis the leaves become more lanceolate and pointed, and 
have two to four prominent recurved spines on either side. The 
margins of all the leaves are strongly cuticularized. 
The ligular epidermis of the leaf of the prostrate axis is composed 
of oblong cells with wavy margins. The aligular epidermis is similar 
in character. Siomata occur on the aligular face only. A few stomata 
occur along the margin where the cuticularized thick-walled cells are 
absent. 
