Osborn. — Some Observations on Isoetes Drummondu , A.Br. 49 
The cells at the extreme base of the sporophyll of Isoetes Drummondii are 
not sclerized. The mesophyll cells at this region become packed with 
starch (Fig. 8) during the vegetative season, and towards its close their 
walls become mucilaginous. 
In transverse sections of the leaf taken near the base of the sporangium, 
it is noticeable that at the initiation of the process there are two centres of 
Fig. 8. Cells from mucilage tissue at base of sporophyll collected in October. The walls are 
already considerably thickened, but some starch remains (cf. Fig. 13). x 173. 
Fig. 9. Microsporophyll in transverse section. Starch-containing cells obliquely shaded, two 
lateral centres of mucilaginous change cross-hatched. x 13*5. 
Figs. 10 a and 10 b. Megasporophyll viewed abaxially (10 a) and laterally (10 b), showing pad of 
mucilage cells extending across base, also extent of tough ‘ shield ’ developed behind sporangium, 
x 2.25. 
Fig. 11. Median longitudinal section of megasporophyll collected in October. Cross-hatching 
shows extent of mucilage tissue, x 13-5. 
mucilage formation to be seen (Fig. 9), placed laterally to the leaf-trace. 
Later these coalesce and a continuous band of mucilage tissue results. 
Owing to this development there is an increase in thickness at the base of 
the leaf (Fig. 10), resulting in the formation of a pad or hump of mucilage 
cells running as a band transversely across the base of the sporophyll, 
tapering at either end and extending upwards behind the sporangium for 
F 
