the Anatomy of the genus Selaginella , Spr, 87 
The marginal papillae of the ligule are, in the young state, 
filled with mucilage, and stand out prominently when treated 
with Bismarck-brown. Further down the axis, and after the 
leaves have reached their maximum development, the ligule 
undergoes considerable change. The cells to a great extent 
lose their contents, and, as I have already shown, become 
thicker-walled and cuticularized, cutting off the ligule in con- 
sequence from further water-supply. 
All the facts in connexion with the ligule point, I think, to 
the function being a temporary one, viz. to act as an organ for 
keeping the growing-point and the young leaves moist. In 
this respect the ligules of Selaginella and Isoetes may be quite 
reasonably compared. Indeed from a morphological point of 
view also the ligules of these two genera seem to be merely 
specialized types of ramentum, although they do not neces- 
sarily form a ground for believing in the close phylogenetic 
relationship of genera otherwise so distinct. 
EXPLANATION OF FIGURES IN PLATE VIII. 
Illustrating Professor Harvey Gibson’s paper on Selaginella . 
S. s pinos a , P. B. 
Fig. 1. Longitudinal section through the growing-point of S. spinosa. x 350. 
The initial cells of the ligule are shaded. 
Fig. 2. Longitudinal median section of a half-grown ligule. X350. The 
sheathing-cells are shaded and have subdivided. 
Fig. 3. Face view (tangential section) of a ligule slightly older than that repre- 
sented in Fig. 2. The sheathing cells are seen end on ; the glossopodial cells, 
eight in number, are followed by the densely granular cells of the body of the ligule. 
x 350- 
Fig. 4. Longitudinal median section through a ligule at a stage of development 
halfway between those represented in Figs. 1 and 2. x 350. 
Fig. 5. Transverse section through the body of a ligule at the stage represented 
in longitudinal section at Fig. 2. x 350. 
Fig. 6. Longitudinal section through the base of an older ligule, showing the 
thickened walls of the sheathing cells, x 350. 
