174 



THE M \K .VI I I All s 



leaf traces with these takes place exactly as in the youngei plant. Fig. 157, 5, shows 

 the separate leal traces and the free axial strand, wink- in ./ the leaf traces are 

 becoming fused with the broad central strands ami tin- axial strand is also anastomos- 

 ing with one ol tin- latter. This lias taken place at tin- point of junction with a 

 root. While 111 the younger sporoph) te the mucilage duets are confined to tin- central 

 region, 111 the older plant they occur also in the peripheral region of the stem (hj>. 

 157, ///). 1 he details ol the vasculai bundles are shown in fi^s. 1 5 S ami 15c). 



n 



Fig. i ^S. — Details ol v.iscular bundles From sections shown in fi^. 156. 

 \ .in. I H .ire the ends of the crescentic bundle shown in fig. 156, l> ; '.'. is .1 leaf trace and I) pari <>t an older bundle. ■. 1 so. 



To recapitulate: The vascular system in the young sporophyte of Dancea 

 begins as a single axial strand, which is continuous through the cotyledon ami mot. 

 At a very early period a second vascular bundle or stele is formed in the second leaf 

 connecting with the primary strand, and this is followed by a similar single strand 

 or stele in each succeeding leaf, up to about the seventh. Up to this time, except 

 for the steles of the secondary roots, the whole vasculai system is built up of united 



in.. 159. 



\, part of central stele; B, the commi ural bundle from a yoi D ijcnmani. 



leaf traces and there is no cauline bundle in the strict sense of tin- word, although 

 we may speak of the bundle, or stele of the stem, as soon as there is a solid central 

 strand formed below the junction of the earlier leaf traces. This primary stele 

 never has the form of a true protostele, however, as tin- xylems belonging to the 

 separate leaf nans can be recognized and the compound nature of this central 

 bundle is unmistakable. 



