550 



SCIENTIFIC AND APPLIED PHARMACOGNOSY 



in the older roots; outer cortex composed of a nearly closed ring of 

 tangentially elongated groups of stone cells, the walls being bright 

 yellow, very thick and marked by prominent branching pores; inner 

 bark composed mostly of starch-bearing parenchyma, and cells con- 

 taining rosette aggregates of calcium oxalate, the phloem occurring 



FIG. 236. Asclepias tuberosa. Butterfly weed, Pleurisy root, Orange Milk- 

 weed. A hairy, perennial herb, very leafy, branching at the summit, and 

 having bright, orange-colored flowers in umbels or flat-topped cymes. 

 After Brown. 



as a narrow strand outside the wood wedges, the latter composed 

 mostly of wood parenchyma and wood fibers among which are dis- 

 tributed a few wide trachese having simple pores; medullary rays 

 very broad consisting of thin-walled, radially elongated starch-bearing 

 cells; pith in rhizome composed of starch-bearing parenchyma, 



