475 
central vascular body, and continually producing new layers of parenchyma- on 
the outside. This takes place especially in two or three directions, so that two or 
three corresponding masses of tissue are formed, slowly dying off on the outside, 
between which lie as many deep furrows meeting on the under surface of the stem. 
From these a large number of roots are produced in rows in acropetal succession. 
In the Selaginelleae the stem remains slender, but lengthens rapidly, branching 
profusely, and forms distinct internodes. The end of the stem rises above the 
youngest leaves as a slender cone. In Selaginella a tendency prevails to sympodial 
scorpioid development of the branches which not unfrequently leads to the system of 
abundantly branched shoots developed bilaterally in one plane attaining a definite 
outline, and a corresponding resemblance to a compoundly pinnate leaf. In con- 
sequence of the small size of the leaves in this 
genus, the general habit is mainly dependent on 
the development of the systems of branches. 
The main shoots which result from the sympo- 
dial development of the branches may creep like 
rhizomes, may grow obliquely upwards, may 
climb, or may form the stems of arborescent 
and fruticose plants. In all cases the repeated 
branchings take place in one plane, for the 
bilateral symmetry which is so marked in the 
position of the branches and in the phyllotaxis 
already exists in the growing point. 
The Leaves are always simple, unbranched, 
penetrated by only a single fibro- vascular bundle, 
terminating in a simple point, and ending, in 
Selaginella^ in a fine awn. The largest leaves 
occur in Iso'e'tes, where they attain a length of 
from 4 to 60 cm. They are in this case divided 
into a basal part or sheath, and an upper part 
or lamina. The sheath does not entirely em- 
brace the stem, but rises in a somewhat trian- 
gular form from a very broad insertion, and is 
acuminate ; it is convex behind and concave in 
front, where there is a large depression, the Fovea, 
containing the sporangium ; the margin of this depression rises in the form of a thin 
membranous outgrowth, which in many species lies above the sporangium and 
envelopes it, the Velum. Above the fovea and separated from it by the * saddle," 
lies a smaller depression, the Foveola, the lower margin of which forms a lip, the 
Labium, while from its bottom an apiculate membranous structure, the Ligule (or 
Lingula), with a cordate base, is prolonged beyond the foveola (Fig. 334, A). The 
lamina of the leaf, containing chlorophyll, into which the sheath passes above, is 
narrow and thick, almost cylindrical, but flattened in front, and penetrated by four 
wide air-canals, which are divided by septa. This form is exhibited by the fertile 
leaves of all the species of Isoeles ; a rosette of such leaves is produced annually ; 
but between each pair of annual whorls is formed a whorl of imperfect leaves, which 
Fig. 334.— .-^ longitudinal section through the base 
of a leaf of Iso'e'tes laaistris with its microsporangiuin 
mi still unripe ; B longitudinal section of the lower 
part of a young sporangium (X 300) (after Hofmeister). 
