286 THE ANATOMY OF WOODY PLANTS 



treatise upon the anatomy of the vascular plants to elaborate at 

 any length the question of the phylogeny of the tubular central 

 cylinder, important as this is for the proper understanding of 

 the higher plants in the light of the doctrine of descent. The 

 whole situation may conveniently be illustrated by reference to 

 the Osmundaceae. In discussing the evolutionary principles 

 involved in the development of the siphonostele in this group, we 



FIG. 203. Transverse section of the stem of Osmundites skidegatensis 



shall appropriately start with types from earlier geological periods. 

 In Fig. 203 is shown a photograph of the central cylinder of a 

 fossil osmundaceous stem from the Lower Cretaceous of Western 

 Canada. In the stem under discussion the magnitude of the 

 stelar system is much greater than that found in any living species 

 belonging to the tribe and, in fact, more clearly resembles the 

 conditions presented in a large stem of a fern of the ordinary type. 

 The pith as well as the cortex is occupied by numerous dark masses 

 of brown sclerenchyma a condition closely resembling the state 

 found in siphonostelic stems of ordinary ferns. An inspection 

 of the periphery of the stele shows the presence of numerous 



