366 West. — A Contribution to the Study of the Marattiaceae. 
based upon a study of these models. But, owing to the difficulty of 
manipulating thin layers of wax of uneven thickness with any degree 
of accuracy, the curvature of the basal portion of the adult rhizome is not 
represented in the large model (PI. XXI, Fig. 1 A). For a similar reason, 
the slight curvature of the apex of the small rhizome, which was about to 
assume its horizontal growth, is not shown in the model represented in 
Text-figs. 4, A, and 5. 
Danaea alata , Sm. The present writer’s observations on the develop- 
ment of the vascular tissues in a large number of very young sporelings 
o i Danaea for the most part confirm the account given by Campbell (20) as 
regards this genus. The vascular strand of the embryo plant is formed 
very early, being first differentiated 
in the cotyledon ; tracheides make 
their first appearance at the junction 
of cotyledon and primary root, and 
from thence the development of the 
tracheides works upwards and down- 
wards until a simple vascular strand, 
continuous from the tip of the coty- 
ledon to the apex of the primary 
root, is produced. The trace of the 
second leaf, which arises nearly op- 
posite the cotyledon (Text-fig. 3, B), 
unites with the primary vascular 
strand in the so-called hypocotyle- 
donary region. As Campbell (20) rightly points out, the strands belonging 
to the first two leaves of the young sporophyte are quite distinct in this 
region, being separated from one another by a very irregular layer of 
small parenchymatous cells. Lower down, however, they appear to form 
a single more or less oval strand (as seen in transverse section) which 
merges insensibly into the diarch bundle of the primary root. A model of 
the vascular system of a young plant which had attained to approximately 
this stage of development is represented in Text-fig. 3, A. It will be noticed 
that there is as yet no sign of a second root. 
Text-figs. 4, A, and 5 represent a model of the stelar system of a rather 
older sporophyte which had developed eight leaves. Traced downwards, 
the simple traces belonging to the third and fourth leaves (Text-fig. 4, A, 
l.t. 3 and l.t . 4) gradually approach and finally coalesce, and still farther 
down join the trace of the second leaf close to its union with the vascular 
strand of the first leaf or cotyledon. The trace of the first adventitious 
root (Text-fig. 4, A, r.t. 2) joins the stem-stele 1 near the point where the 
traces of the third and fourth leaves become united. Thus, in the young 
1 The convenient descriptive term ‘ stem-stele 7 is here employed for the common vascular tissue 
produced by the close association or union of the earlier leaf- and root-traces. 
Model of the stelar system of a very young 
sporeling. Side view. l.t. i, It. 2, leaf-traces. 
b. Diagram showing divergence of the first two 
leaves. 
