124 
MORPHOLOGY 
leaves), each one having at base a mass of sporogenous tissue (sporangium). 
This final structure is the simple Lycopodium body just described. It is the 
so-called Selago type, in which all or nearly all the leaves are sporophylls, and 
hence practically the whole body is a strobilus. It must be understood that this 
proposed origin of the Lycopodium sporophyte is simply a theory, but it is a 
very suggestive one. 
The more complex sporophytes of Lycopodium are branching bodies 
(fig. 265). There is a gradual sterilization of the lower sporophylls, 
which thus become simply foliage 
leaves. Finally the sporophyte 
becomes differentiated into two 
distinct regions : that bearing 
foliage leaves and that bearing 
sporophylls. The sporophylls 
finally become quite different 
in appearance from the foliage 
leaves and are organized into 
a compact strobilus, which is 
sometimes separated from the 
branching leafy body by a long 
stalk bearing only rudimentary 
leaves (fig. 266). 
Vascular system. The anat- 
omy of the stem emphasizes 
further the primitive character 
of this sporophyte. A cross 
section shows two regions : the 
cortex, an outer region of living 
cells ; and the central cylinder 
or stele, in which the vascular 
system (conducting system) is 
developed. The vascular system 
FlG. 266. Lycopodium complanatum: a nas been f oun( j to fcc o f great 
importance in any study of the 
evolution of vascular plants, 
and, therefore, the outline of its history must be indicated. In the 
simpler lycopodiums, or in young stems, the vascular system of the 
stem forms a solid axial cylinder, in which the xylem (the group of 
water-conducting vessels) is completely surrounded by the pMoem 
sporophyte showing distinct differentiation be- 
tween foliage region and strobilus. 
