3 
Anatomy of the Ophioglossaceae. III. 
not be dealt with here. This paper will be limited to the anatomy of the 
developed regions of young and adult rhizomes, and the facts will be 
conveniently described in the following order: 
1. Some points in the anatomy of the adult rhizomes. These include 
the relative development of centripetal and centrifugal xylem, the vascular 
attachment of the roots, the origin of the leaf-trace and its structure until 
after the first division in the cortex, variants in type of leaf-trace, and the 
disturbance of the vascular structure in relation to the vestigial buds. 
2. The anatomical relations of actual branches to the main rhizome, 
and the associated development of accessory or secondary xylem. 
3. The structure of the stele and leaf-trace in small rhizomes with the 
juvenile type of structure, whether arising as branches, or as young plants 
developed from an embryo ; the progression from the juvenile to the adult 
type of structure, and condensation of stelar structure from the adult to the 
juvenile type. 
The distinction made above, between the adult and juvenile types of 
rhizome and stele, is of practical convenience, but cannot of course be 
definite. Rhizomes, the stele of which has a pith and a clear distinction 
of outer and inner metaxylem, both consisting of pitted tracheides, will be 
classed as adult; those in which the stele is solid, or if medullated has no 
definite inner metaxylem composed of pitted tracheides, as juvenile. The 
transition from the juvenile to the adult type of stele is associated with an 
increase in the diameter of the rhizome, but the adult type is found in 
rhizomes of a wide range in thickness. 
I am greatly indebted to Prof. F. W. Oliver and Prof. Bower for 
interesting pieces of rhizome of Helminthostachys. 
1. Some Points in the Anatomy of the Adult Rhizome. 
The general features of a transverse section of a large rhizome of 
Helminthostachys are illustrated in Text-fig. 1, B. This shows the pro¬ 
portional sizes of the rhizome and stele, and the distinction between the 
dorsal side of the rhizome, where the remains of the attachment of an old 
leaf-sheath are seen, and the ventral side, where two large laterally placed 
roots are attached. The section has passed through the stele, where the 
xylem of a nascent leaf-trace has just become detached from the stelar 
tube on the side away from the median line. On the other side of the 
median line is seen the vascular disturbance, in relation to the vestigial bud 
belonging to the leaf next behind. The stele is surrounded by the external 
endodermis, which is only interrupted in relation to the vestigial bud, while 
the pith is delimited by a well-marked endodermis. 
The convention adopted in this figure for representing the position and 
extent of the various tissues is maintained in many of the other text-figures, 
and may be explained once for all. The external endodermis is represented by 
B 2 , 
