y6 G Wynne- Vaughan. — Observations on the 
continuous ring of a white or grey colour, situated in the midst 
of the yellowish-brown ground-tissue at a distance from the 
centre of about a third of the radius (Plate III, Fig. i). The 
ground-tissue is almost entirely composed of vertically elon- 
gated cells with square or bluntly pointed ends. The cell- 
walls are well thickened, with numerous round simple or 
slightly bordered pits, and are impregnated by some colour- 
ing substance to which is due the general brown appearance 
of the section. The cells of the epidermis, though less elon- 
gated vertically, do not differ from those of the ground-tissue 
in the structure of their walls or in the colour. Sclerenchy- 
matous cells such as these compose the whole of the ground- 
tissue of the stem, with the exception of a few layers of 
parenchyma with thin, colourless, and unlignified walls, inter- 
vening between the endodermis and the sclerenchyma on 
either side of the solenostele (Fig. 2, a ) ; and again of a 
few similar parenchyma- cells that are found irregularly 
scattered in small groups and strands in the midst of the 
sclerenchyma itself. These small parenchymatous islets in 
the sclerenchyma only occur in the neighbourhood of the 
solenostele, becoming fewer the farther away from it on either 
side. In longitudinal section it is seen that the cells of which 
they are composed are much shorter than those of the thick- 
walled ground-tissue, that they have rounded outlines forming 
conspicuous intercellular spaces, and that they are arranged 
in vertical rows of various lengths, which appear to arise, in 
the apical region, by rapid and long-continued division in 
certain cells, while the rest grow on without further division. 
As regards the general sclerenchyma the cells have thinner 
walls and wider lumens at the very centre of the stem, and in 
the median region of the cortical ground-tissue (that lying 
without the solenostelic ring) than elsewhere (Fig. 1). The 
occurrence of these scattered islets of parenchyma among the 
sclerotic general ground-tissue of the stem is an interesting 
peculiarity, and I believe one of very rare occurrence among 
the Ferns, the only other instances which I have hitherto 
come across being in the stems of Dicksonia apiifolia , Hk., 
