KRAMERIA CANESCENS. 



21 



chlorophyll-bearing' tissue is the subepidermal band which extends to the 

 interrupted ring of hard bast. Chlorophyll is also to be found in the 

 medullary rays and in the outer cells of the pith. 



The chlorophyll band is composed of a single layer of much-elongated 

 palisade cells, or of a single layer of palisade cells and one tier of nearly 

 cuboid cells which lie within, /. e., towards, the woody cylinder. 



FIG. 9. Krameria cancscens: A, transverse section of leaf, showing char- 

 acter of the subepidermal palisade cells; B, cross-section of stem, to show 

 structure of cortical chlorophyll band; same magnification as in A; ch. b., 

 cortical chlorophyll band; h. 6., hard bast; med., medullary rays. 



With increase in diameter, up to 2.5 mm. and 30 cm. from the tip, there 

 is no marked change in the appearance of the chlorophyll apparatus of the 

 stem, but in a branch 3.5 mm. in diameter and 40 cm. from the tip a marked 

 modification is found. This is largely owing to the formation of cork. 

 The phellogen arises in the parenchyma between the hard bast and the cam- 

 bium and by its activities cuts the entire chlorophyll band off from the 

 living portions of the stem. As an immediate consequence the chlorophyll 

 band becomes at once a portion of the cork. In a branch 2.5 mm. in diam- 

 eter no chlorophyll was found in the wood or pith and none also in the 

 most inner portion of the cortex. It was confined to a layer of cells, or to 

 two layers, immediately beneath the phelloderm. 



The following measurements were made: 



