132 MORPHOLOGY 



tuberous region and an aerial, green, more or less lobed region bearing 



the sex organs. 

 Conclusions. Since Lyco podium 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 

 concentrically arranged. The sporangia are large 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. Phyllo- organs. The antheridia develop endogenously, and 



bta'rktg' a^Ttalked the s P erms are bryophytic in type. The archegonia 



strobilus. are also embedded, as in Anthocerotales. 



Selaginclla 



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 heterospory (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 ligulej 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 



