lovejoy: anatomy of g^rtneria. 285 



StypheUa Ixta, of the family Epacridese. The collenchymatous 

 cells, lying two to three layers deep, are of the typical sort, 

 and also contain chloroplasts in sufficient numbers to be of 

 significance in photosynthesis. 



Epidermis. 



The epidermis of the stem, as that of the leaf, is beset with 

 clothing and glandular hairs. Here, however, the short gland- 

 ular hairs are much more numerous than on the leaf. They 

 each have the same general structure as those on the leaf, 

 hence no discussion of that is necessary here. 



The epidermis of the stem occurs as a single layer of cells, 

 elongated longitudinally, and having, in the very young stem, 

 walls of cellulose. As the stein becomes old the walls thicken, 

 and there is produced a cutin layer. 



A curious exfoliating process, whereby the cambium forms 

 cork and chlorenchyma rings, which replace the secondary 

 pericycle chlorophyllous tissue, just as the latter replaced the 

 first cortex chlorophyll tissue, is reported by Cannon, W. C. 

 (1908), as peculiar to Giertneria, and to be repeated several 

 times until in the oldest parts of the branch the portions cut 

 off and those reformed no longer contain chlorophyll. 



THE ROOT. 



The root system of Gsertneria (in keeping with character- 

 istic xerophytic structure) is well developed. The older roots 

 are seen to have a deeply furrowed, rough, coarse outer cover- 

 ing, and are so very hard as to permit of no thin sectioning, 

 even after having been disilicified for some weeks. In cross 

 section of the very young root appears a central xylem cyl- 

 inder, which is highly lignified and surrounded by a phloem 

 ring, which in its turn is surrounded by a pericycle averaging 

 five cells in thickness, in which are irregular groups of stone 

 cells. Around the pericycle is the primary cortex, averaging 

 seven or eight cells in depth. These have suberized cell walls, 

 and appear to be in the process of direct transformation into 

 cork; no definite cork cambium is to be observed. However, 

 the inner of the suberized cells were still alive, having in them 

 functioning nuclei. (See fig. 55.) 



The epidermis is a single layer of cells. (See figs. 53 and 54.) 

 One peculiarity of the root hairs is that they retain their place 

 long after the inner tissues have become suberized and they are 

 functioning no longer. (Figs. 47, 53, and 54.) 



