132 
MORPHOLOGY 
tuberous region and an aerial, green, more or less lobed region bearing 
the sex organs. 
Conclusions. Since Lycopodium and its ally represent possibly the 
most primitive vascular plants, a summary of the important features 
will be useful. It would follow that the most primi- 
tive leafy sporophyte is a strobilus, in the sense 
that all its leaves are sporophylls. The first foliage 
leaves are small and scattered, and are sterilized 
sporophylls. The vascular system consists of a 
single, solid cylinder, whose xylem and phloem are 
concentricall y arranged . The sporangia are 1 arge and 
solitary on the adaxial face of the sporophyll, and 
each one is developed from a transverse row of initial 
cells. The new structures of this sporophyte, as con- 
trasted with that of the bryophytes, are sporophylls, 
foliage leaves, vascular system, root, and suspensor. 
The gametophyte is a subterranean tuberous 
body with an aerial, green crown bearing the sex 
FIG. 295. Phyiio- organs. The antheridia develop endogenously, and 
flossum: sporophyte ., i i .. mi 
bearing a stalked the s P erms are bryophytic in type. The archegoma 
strobilus. are also embedded, as in Anthocerotales. 
Selaginella 
General character. This is the great genus of modern Lycopo- 
diales, comprising nearly 500 species, which belong chiefly to the 
tropics. It is evidently closely related to Lycopodium, and may be 
regarded as a modern representative of forms that lived during the 
coal measures, and that had developed helerospory (see below). 
Sporophyte. The sporophyte body resembles that of Lycopodium 
in habit (fig. 296), although it is usually much more delicate. It 
is characterized by two noteworthy features. One is the development 
of a ligule, a flaplike outgrowth from the adaxial surface of the leaf 
near its base. The ligule is an embryonic organ of the leaf, being 
very prominent and functional during the growth of the leaf blade. 
When the blade matures, the ligule becomes merely an inconspicuous 
and membranous flap. This curious structure is a feature of all the 
Lycopodiales (including fossil groups) except Lycopodium and Phyl- 
loglossum, and for this reason the former are often called Ligulatae, to 
distinguish them from the latter, which are Eligulatae. The other 
