OF THE EASTERN UNITED STATES 363 



very slightly angular in transverse section. Some of them show the 

 presence of the Actinomyces organism. Alike with those of the root, they 

 e.xhibit barred septa. Their distribution in the spring, summer and 

 autumn wood is strikingly uniform. The numerous wood fibres are 

 narrow, elongate and taper ended. Their walls show many oblique pits. 

 The wood parench>Tna cells are elongated in the direction of the long 

 axis of the stem and show slightly thickened walls. 



The pith region is composed of rounded to polygonal parenchyma 

 cells, whose walls become lignified very early. Some of them contain 

 a brownish-yellow substance (gummy lignin) while others contain starch 

 grains. Protoplasmic processes extending from cell to cell are quite 

 prominent. 



Subterranean Branch of Myrica cerifera, L. 

 The rhizome of Myrica cerifera differs histologically from the aerial 

 stem in the following particulars: — There are fewer layers of cork and 

 more layers of cortical parench\Tne cells. In transverse section the 

 cortex cells appear more rounded, less tangentially elongated. The 

 intercellular air-spaces are somewhat larger. No crystals of calcium 

 oxalate have been found either in the cortex or pith. There are generally 

 more cells containing gummy lignin. Sclerenchyme elements are 

 entirely wanting in the cortex. A discontinuous zone of sclerenchyme 

 is present in the pericycle, composed of numerous small islets of peri- 

 cambial fibres. The phloem region shows fewer bast fibres. The 

 medullary-ray cells are broader and have thinner walls. The tracheae of 

 the xylem are fewer and for the most part about twice as broad. The 

 largest have a maximum breadth of 57.6 n, while the largest of the aerial 

 stem are 38.4 fx. In some of these the writer has observed colonies of 

 coccus-like structures which probably represent an involution form of the 

 Actinomyces previously discussed. The pith cells are about twice as 

 large, contain more starch and have considerably thinner walls. 



Aerial stem of Myrica Carolinensis, Miller 



Passing from periphery toward the centre the following structures 

 can be observed: — 



1. Cork of several layers of brick-shaped cells, whose cell walls are 

 either suberized or lignified or in part suberized and in part lignified. 

 There is a tendency for more lignification to occur in this region than in 

 that of the aerial stem of M. cerifera. 



2. Phellogen of a single layer of thin-walled tangentially elongated 

 cells. 



