OF THE EASTERN UNITED STATES 361 



Primary Striuture 



(M. cerifera, M. Carolinensis, M. Macfarlanei, M. Gale, and 



Comptonia asplenifolia) 



The epidermis of the young stems is covered by a cuticle more or less 

 thickened according to the species. The stomata are comparatively few 

 and frequently elevated. Hairs analagous to those of the leaves are 

 found in large numbers and are especially numerous on the distal extremi- 

 ties {vide supra). 



The cortical parenchyme is composed externally of cells containing 

 chloroplasts. Internal to these are cells which during periods of rest 

 contain many starch grains. Certain thin walled cells are very rich 

 in tannin content, which may be readily determined by the use of ferric 

 chloride solution which imparts a bluish-black color to this substance. 

 Other cells of this region contain crystals of calcium oxalate in the form 

 of rosettes, tabular monoclinic prisms, or crystal sand. Hambright and 

 Moore have found in the cortex of Myrica species traces of gum, resin, 

 volatile oil, palmitic and myristic acids. Beringer has observed and 

 figured "secretory resin cells" in the cortex of Comptonia asplenifolia. 

 Chevalier (7, p. 103) and the writer have found these "secretory resin 

 cells" of Beringer to be nothing other than dead cells filled with gummy 



lignin. 



The pericambium consists of polyhedral cells of uniform size and 

 formed opposite each of the fibro-vascular patches. Very early many 

 cells of this region become thickened in their walls through the deposition 

 of lignin. The primary conducting system is composed of 10 cauline 

 fibro-vascular bundles which form in the internode a lobed gamostelic 

 ring. These bundles break up in the vicinity of the nodes to furnish 3 

 veins running into each leaf. In the crown one is able to distinguish up 

 to 19 apparent conducting masses separated by very large medullary- 

 rays. At each node, the crown bundles split up in the region of leaf 

 insertion. At first a large cord of wood and bast becomes de- 

 tached, then, a Httle higher two smaller cords separate, which take up 

 their position, respectively, to the right and to the left of the first. The 

 gamostele closes up after first filling in the gap left by the departure of 

 the lateral bundles. 



In each procambial cord the first phloem elements consisting of sieve 

 tubes, companion cells and phloem parenchyme cells may be distin- 

 guished in contact with the pericambial arc. The primitive tracheae 

 appear later in contact with the pith parenchyme. The woody fibre 

 differentiation of the procambial parenchyme, corresponding to the bast 



