KQEBERLINIA 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. 
Fic. 8.—Ke@berlinia 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. Ifit 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 
