1906] WEISS—BARK IN SASSAFRAS 435 
from the layer of parenchyma just within the epidermis. He also 
remarks that the secondary bast fibers, although usually scattered, 
‘form distinct strands in certain genera, and that the individual fibers 
are normally four-sided in cross section with narrow lumina. 
The present investigation is based on material collected near New 
Haven, Connecticut, and is confined to the stem and its branches, no 
reference being made to the bark of the root. The tissues described 
may be classified as follows: . 
PRIMARY TISSUES SECONDARY TISSUES 
Epidermis Tissues derived from the cambium ring 
Outer cortex The phellogen and its derivatives 
Primary medullary rays 
Primary bast 
PRIMARY TISSUES. 
Epidermts. 
The epidermal cells are characterized by a strongly thickened 
cuticle. Close to the growing point they are isodiametric and thin- 
walled, but the cuticle begins to make its appearance very early and 
OADOOSD 
SSeS POR ESOC e 
Satya OBE 
=a cS i> Ba SC <4 s 
SORTS ORo Ey 
<> 
aes Semel scenessios *) 
ie I Fa hee 
Pom ; Cre ac 
hey 
AN 
}} 
hy 
| 
iS 
2, 
a 
Re) 
(y 
rai 
. tf ce 
Fic. 1.—Cross-section through bark one year old. X70. cam, cambium ring; 
¢, epidermis; m, medullary ray; p, parenchyma; phx, primary phloem; s¢s, primar) 
sclerenchyma; sc,, secondary sclerenchyma; st, stone cells; x, xylem. 
Practically completes its development during the first year’s growth. 
At the close of this period it occupies about half the thickness of the 
epidermis (jig. 1). During the elongation of the stem the epidermal 
cells retain the power of growth and division. Since their growth is 
largely in a longitudinal direction, the cell-division is mainly brought 
about by transverse walls, division by longitudinal walls being much 
