Davey.— Seedling Anatomy of certain Amentiferae . 581 
leaf is prominent at an early stage and causes slight asymmetry in the 
structure of the node. 
Myrica ccilifornica (Fig. 18, in). The cotyledon petioles each possess 
a double bundle whose metaxylem and phloem diverge so as to be laterally 
placed with respect to the median protoxylem. At the node this proto- 
xylem occupies the cotyledonary plane with metaxylem spreading tangen- 
tially on either side of it. In the upper part of the hypocotyl the stele 
conforms to the diarch type (see p. 577). The central protoxylems with 
their adjacent metaxylem wings constitute xylem arcs or secants in the 
cotyledonary plane, while the four phloem groups occupy the diagonal 
corners. In the intercotyledonary plane are the traces of the first and 
second plumular leaves, slightly differentiated as regards primary elements, 
Figs. 2 and 3. Myrica californica . 2. Transverse section of hypocotyl near cotyledonary 
node, x 280. 3. Transverse section of root. X320. ph. = phloem ; cot. = cotyledonary plane; 
intercot. — intercotyledonary plane ; px. = protoxylem. 
but linked with neighbouring cotyledonary traces by cambium which 
produces two bands of vascular tissue leaving wide gaps outside the proto- 
xylem poles in the cotyledonary plane. In descending the hypocotyl this 
secondary tissue dies out. The phloem of the plumular trace persists for 
a time ; it becomes divided, and its halves unite with the adjacent cotyle- 
donary phloems. In the intercotyledonary plane feebly differentiated 
protoxylem elements appear, with metaxylem spreading tangentially on 
either side of them and increasing in amount as the hypocotyl is de- 
scended (Fig. 2). A tetrarch stele results, with protoxylems at the cotyle- 
donary and intercotyledonary poles flanked by tangentially spreading meta- 
xylems which eventually meet so as to form a lignified ring around the 
pith (Fig. 3). A well-differentiated endodermis is present. The stele 
R r 
