154 Gibson . — Contributions towards a Knowledge of 
few not extremely important exceptions noted, all the species 
with heterogeneous leaf-epidermis belong to the dorsiventral 
monostelic or allied tristelic types ; whilst those with two 
laterally-placed steles have homologous leaf-epidermis. With- 
out pressing the point too much, one may, I think, say that, 
on the whole, a classification of these fifty-two species based 
on the anatomy of the stem is supported by the structure of 
the leaf. 
EXPLANATION OF FIGURES IN PLATE IX. 
Illustrating Professor Harvey Gibson’s paper on the leaf of Selaginella. 
Fig. i. A trichome from the margin of the ventral leaf of S. Douglasii , with 
basal investment of marginal cells, x 350. 
Fig. 2. Adjacent stomata of S. viticulosa. x 350. 
Fig. 3. Thick-walled stomata of S. Martensii. x 350. 
Fig. 4. Margin of the ventral leaf of S. serpens, showing semi-occluded uni- 
cellular spines, x 350. 
Fig. 5. Stoma of S.producta, showing great thickening in surrounding epidermal 
cells, x 350. 
Fig. 6. Aligular epidermis of the ventral leaf of S. producta. The cells have 
localized thickenings. X350. 
Fig. 7. Stoma of S. concinna , with almost occluded guard-cells, x 350. 
Fig. 8. Stoma of S. Galeottii. x 450. 
Figs. 9, 10. Stomata of S. viticulosa. One is figured with three guard-cells, 
x 350- 
Fig. 11. Aligular epidermis of ventral leaf of S. patula. One of the warty 
sclerotic fibres is shown, x 350. 
Figs. 12, 13. Development of stomata from a young dorsal leaf of S. uncinata. 
x 550- 
Fig. 14. Marginal spine of S. serpens, x 350. 
Fig. 15. Multicellular trichome from the basal lobe of the ventral leaf of 
S. sulcata, x 450. 
Fig. 16. Sclerotic fibre with two rows of warts from the aligular face of the 
ventral leaf of A. viticulosa. x 350. 
Fig. 17. Transverse section of the ventral leaf of S. Lyallii. x 350. (For 
description see text.) 
Fig. 18. Transverse section of the ventral leaf of S. delicatissuna. x 350. 
