366 Gibson.— On Siliceous Deposit in Selaginella . 
EXPLANATION OF FIGURES IN PLATE XVIII. 
Illustrating Mr. Harvey Gibson’s paper on Siliceous Deposit in Selaginella. 
All the figures are drawn under a magnification of 350. 
Figs. 1-5. S. Martensii, Spr. var. compacta. 
Fig. 1. Surface view of the siliceous plates from the cortical wall of the lacuna 
of a fully-developed stem. 
Fig. 2. Siliceous plates on the cortical wall of the lacuna in section. 
Fig. 3. Young stages in the development of the plates, taken from the stem 
about a quarter of an inch from the meristem region. 
Fig. 4. Isolated plates from the apex of a young stem after treatment with 
concentrated sulphuric acid. 
Fig. 5. Transverse section though the cortex after clearing in eau de Javelle 
and mounting in balsam. (The dark shading indicates the siliceous deposit.) 
Fig. 6. Trabecula of S. Martensii , var. stolonifera , showing distribution of 
silica between the median cells of the trabecula. 
Fig. 7. Isolated siliceous plate from a mature stem of S. Martensii , var. 
Jlexuosa, showing two apertures for the exit of the basal cells of trabeculae. 
Figs. 8-10. S. grandis, Moore. 
Fig. 8. Siliceous plates from the cortical wall of the lacuna of the mature stem 
at the level of an internode. 
Fig. 9. Siliceous plates from the cortical wall of the lacuna at the origin of a 
branch. 
Fig. 10. Transverse section of the inner cortex of the mature stem. The dark 
shading indicates the siliceous deposit. 
