THE ANGIOSPERMAE : STEMS 



911 



Fig. 893.— Diagrams illustrating the probable origin of the herbaceous 

 type of stem. A, Woody stem with all rays narrow. Crosses 

 indicate protoxvlem. Bundles in solid black, next to the pith, 

 become leaf traces. B, Herbaceous stem derived from A by 

 conversion into parenchvma of segments alternating with the leaf 

 traces. C, Woodv stem with broad foliar rays. D, Herbaceous 

 stem derived from C bv increase in width of broad rays and 

 decrease in their radial' extent. E, Woody stem with all rays 

 narrow and continuous protoxylem ring. F, Herbaceous stem 

 derived from E bv decrease in cambial activity. G, Woody stem 

 with narrow ravs aggregated opposite the protoxylems. H, 

 Herbaceous stem derived from G by conversion into parenchyma 

 of the segments opposite the leaf traces (JeflFrey). {After Stnnott 

 and Bailey.) 



