PAST HISTORIES OF PLANT FAMILIES 139 



To supply the vascular tissues of the leaf traces, 

 simple strands come off from the outer part of the pri- 

 mary wood, where groups of small-celled protoxylem 

 project (see px in fig. 97). The leaf strands It move 

 out through the cortex in considerable numbers to supply 

 the many leaves, into each of which a single one enters. 



Fig. 97. Transverse Section of Outer Part of Primary Wood of Lepidodendron, 

 showing px, projecting protoxylem groups ; It, leaf trace coming from the stele and 

 passing (as It 1 ) through the cortex 



As regards the fructifications of Lepidodendron much 

 could be said were there space. The many genera of 

 Lepidodendron bore several distinct types of cones of 

 different degrees of complexity. In several of the 

 genera the cones were simple in organization, directly 

 comparable with those of the living Lycopods, though 

 on a much larger scale (see p. 67). In some the spores 

 were uniform, all developing equally in numerous tetrads. 

 The sporophyll was radially extended, and along it the 



