RELATION OF LEAF TO AXIS 197 
formation of a regular stele: in which case the leaf-traces, represented in 
the first case by the protoxylem-strands, would be phylogenetically prior : 
the central metaxylem, on the other hand, would be a later formation, 
developed in the larger forms to furnish additional conducting channels to 
Fic, 99 
A forked sporangiferous branch of Lycopodium chamecyparissus in longitudinal section, 
slightly magnified. =the axile vascular body. 6é=leaves. ss=young sporangia. 
supplement the protoxylems in supplying the needs of the higher foliage 
leaves and sporophylls. 
In approaching an opinion on such a question much will turn upon the 
initial relation of the leaf to the axis in the evolution of the leafy sporo- 
phyte, a matter already discussed in Chapter XI, If the leaf were from 
the first a preponderating influence in the shoot, then the latter explanation 
