19 
Anatomy of the Ophioglossaceae. III. 
fragment of a full-sized rhizome. It bore laterally a small shoot of pale 
colour, with healthy-looking tissues. The parent fragment had evidently 
been displaced in the soil, and the developing lateral branch had adjusted 
its direction of growth to the new position, and had grown out almost at 
right angles to the main rhizome (cf. Text-fig. 5). The interpretation of 
the anatomical relations between the main rhizome and branch was thus 
more complicated than in the first specimen. The altered direction of the 
branch stele had, however, the great advantage of giving a view of its basal 
region in longitudinal section, while the parent rhizome was studied in 
a complete series of transverse sections. 
The fragment of rhizome had the fully adult type of structure, and 
included portions of four leaf-gaps; the first gap was open at the basal end, 
while the fourth gap was not closed when the fragment ended. Vestigial 
buds were present in relation to the first and third gaps, while the actual 
branch occupied the same position relatively to the second leaf-gap. The 
general structure of the stele resembled that of the large adult rhizome first 
described (cf. PI. II, Photo 25). Inner xylem was present, though not so 
strongly developed, and no internal endodermis was recognized. The 
peculiarities of the leaf-trace have already been described (cf. PI. I, 
Photos 11-13). The vascular changes accompanying the closure of the 
leaf-gap resembled on the whole those in the large rhizome described, 
and involved the formation of a large bulge of xylem behind the vestigial 
bud. The bud itself, i. e. the inner end of the canal, was on this rhizome 
situated relatively further forward, and the branch will be seen to stand 
beside a leaf-trace, the departure of which is far advanced. The main 
features of the rhizome are shown in Text-figs. 5 and 6. 
In this case, as in the first branching specimen, the influence of the 
development of the branch extends backwards to the region of the stele, 
where the subtending leaf-trace is just becoming evident. This influence 
is expressed in the same way, namely, by the development of accessory 
xylem outside the ordinary outer primary metaxylem. In the preceding 
specimen this was only developed in such positions that it appeared to pass 
off entirely as the outer xylem of the branch stele. But in this larger 
rhizome the development of accessory xylem was not confined to the 
neighbourhood of the leaf-gap, but extended all round the stele. Further, 
the accessory xylem did not wholly pass off to the branch, but was present 
for a considerable distance after the departure of the branch. It thus 
presented an even more striking resemblance to secondary thickening than 
in the former case. 
It will be convenient to describe the features of this accessory xylem 
more in detail before considering the origin of the branch. Its distribution 
will be evident from Text-fig. 6, in which it is indicated by cross-hatched 
shading. In the first section (a) of this figure, it is seen to be represented 
