2 5 
Anatomy of the Ophioglossaceae . Ill\ 
myself. Some redescription is however necessary, since I am unable to 
agree with Campbell’s interpretation of the structure, or with his view of the 
constitution of the stele of the young and old plants. 
Anatomy of the branches. Both the branches, the connexions of which 
with their main stems have been described, were much smaller than their 
respective parent rhizomes. Their stelar anatomy approximated to that of 
embryonic plants, but was easier of interpretation, since the vascular 
elements were more numerous. They had the further interest of a known 
continuity of the tissues of their steles with the corresponding regions of the 
parent stele. The first branch was followed in a complete transverse series, 
while the lower region of the second branch (including the origin of the 
first leaf-trace and first root) was cut longitudinally, and the remaining 
portion transversely. 
The origin of the first branch has been traced to the stage at which its 
stele (just before attaining a definite cortex of its own) lay beside the 
decaying broken end of the parent fragment (Text-fig. 4, J ; PI. II, Photo 24). 
The stele of the branch, thus completely organized, had a cylinder of xylem 
slightly oval in transverse section, and around this a zone of tissue some five 
or six cells deep, enclosed by the complete endodermis. Presumably 
pericycle, phloem, and conjunctive parenchyma were represented in the zone 
between the endodermis and the xylem, and the sieve-tubes soon become 
recognizable in the transverse section. The chief interest is, however, in the 
constitution of the xylem. This was solid, in the sense of having no definite 
pith, though parenchymatous cells were scattered through it. There was 
a clear distinction between outer and inner or central xylem. The 
tracheides of the zone of outer xylem (Photo 24, x.o.) were larger, and 
showed a roughly radial arrangement like that found in the outer xylem 
of the adult type of stele ; their walls were pitted. The tracheides of the 
inner xylem (Photo 24, x.i.) were smaller, stained less deeply, and their walls 
were reticulately or spirally thickened. 
Judging by the appearance of the elements of xylem, it would be 
natural to regard the stele as centrarch, i. e. as having a central group of 
protoxylem elements surrounded by a zone of metaxylem. The backward 
connexion of these two components of this stele has, however, been shown 
to be with the inner and outer (accessory) xylem of the main axis, 
respectively. That this connexion indicates the right interpretation of 
the stele of the branch is confirmed as soon as preparations for the 
departure of the first leaf-trace become evident. A small group of elements 
now recognizable at the limit between the outer and inner xylem is un¬ 
doubtedly the protoxylem of the nascent trace, and its position demonstrates 
the mesarch construction of the small stele. This stage is represented in 
PL III, Photo 30. The leaf-trace xylem is thus derived from a small arc 
of the outer xylem, with a protoxylem group on its inner face, and as 
