OF THE EASTERN UNITED STATES 367 



ary med. rays); a few (primary med. rays) vary from 1-2 to 1-4 rows 

 of cells in width. The cells of these medullary-rays exhibit marked 

 protoplasm connections which are best seen in a radial longitudinal 

 section. Their walls are lignified. The wood wedges are composed 

 mostly of tracheids with bordered pits. The tracheae are generally 

 pitted and mostly found in the spring wood. Like those of the other 

 stems treated, they show barred septa. They are arranged radially 

 and are more or less polygonal in transverse section. Some of them 

 show a bacterioid content. Spiral tracheae, as in the other stems, are 

 found in the protoxylem. 



8. The pith, as noted by Gris,^^ is composed of thick walled cells 

 which are mostly functionally active. Some of them contain gummy 

 hgnin. 



Subterranean Branch of Myrica Gale, L 



The subterranean branch of this plant differs microscopically from 

 the above ground stem in the following particulars: — The cork zone is 

 narrower. The cells of the cortex are somewhat larger and show fewer 

 crystals of calcium oxalate. There are more tracheids and fewer spiral 

 ducts in the protoxylem. The pitted tracheae with bacterioid contents 

 are more numerous. The tracheae tend to become larger. 



Aerial Stem of Comptonia Asplenifolia, (L.) Alton 



Passing from exterior toward the centre one notes the following 

 structures: — 



1. A cork consisting of several layers of irregularly brick-shaped 

 cells which stain unevenly with safranin and methyl green. Many of 

 them have their inner tangential walls more or less lignified. 



2. A cork cambium (phellogen) of thin walled meristematic cells. 



3. A cortex of tangentially elongated parenchyme cells, some of 

 which contain starch, others gummy Hgnin, tannin or crystals of calcium 

 oxalate of rosette or tabular form. 



4. A pericycle displaying an almost continuous zone of sclerenchyme 

 elements. 



5. A phloem containing numerous more or less oval shaped groups 

 of bast fibres arranged in interrupted circles and separated from one 

 another by the soft bast elements. (Plate 87. Fig. 22.) Each group 

 of bast fibres is surrounded by a number of crystal fibres whose cells 

 contain monoclinic prisms of calcium oxalate. Considerable tannin 

 is evidenced by the use of ferric chloride test solution. The phloem 

 medullary rays are 1-5 rows of cells wide. 



