STEM STRUCTURE 



175 



duces more cork than phelloderm, and the latter 

 tissue may occasionally be reduced to a single layer 

 of cells. In powdered materials cork cells are usually 

 apparent on surface view, and occur in thick masses 



PLATE 59 Continued. 



B. Chionanthus, stem bark. 1. Bark parenchyma (transverse view), contain- 

 ing starch, crystals and resin masses. 2. Bark parenchyma crossed by medullary 

 ray cells. 3. Medullary ray cells. 4. Fibers. 5. Fibers showing branching pores. 

 6. Cork tissue. 7. Stone cells. 8. Bark parenchyma (longitudinal view). 9. Crys- 

 tals. 



of dark color in which definite cell structure is visible 

 only with difficulty (Plate 59). The phellogen and 

 phelloderm tissues are never apparent in powdered 

 materials. 



