KCKBKRLINIA SPINOSA . 



19 



a ring of mechanical tissue composed of hard bast connected by grit-cells, 

 and within this ring- is the thin-walled parenchyma, which separates the 

 hard-bast ring- from the cambium. Medullary rays reach to the ring of 

 mechanical tissue. The wood and the pith exhibit no features of interest in 

 this study. 



FIG. 8. Kivberlinia spinosa: Segment from cross-section 

 of stem 1.5 mm. in diameter, to show distribution of 

 chlorophyll. 



The chlorophyll is practically wholly limited to the cortex. If it is found 

 in the wood at all it is in the outermost medullary rays. The most impor- 

 tant chlorophyll-bearing tissue is the subepidermal band which occupies 

 the area between the epidermis and the hard-bast ring. The outer cells 

 are palisade in form; the inmost three layers are spongy chlorenchyma or 

 they may be elongated in a tangential direction. The parenchyma, which 

 occurs opposite the grit-cells, and therefore between the hard-bast groups, 

 although forming a part of the chlorophyll band, are morphologically the 

 outer ends of the cortical medullary rays . The cells referred to are exterior 

 to the grit-cells and have become detached from the medullary rays by the 

 assumption of heavy walls by that part of them which lies between the 

 hard-bast groups. 



With increased diameter certain changes in the relations of the chloropyll- 

 bearing tissues of the stem take place. The heavy cuticle becomes ruptured 

 at frequent intervals and the spaces thus formed are covered by a many- 

 layered periderm. The cork-cambium arises in the epidermis. As more 



