5 i 
Anatomy of the Ophioglossaceae. III. 
(in which the stele has a large and definite pith and a well-developed inner 
xylem consisting of pitted tracheides) is to be regarded as a process of 
further expression or elaboration of the structure found in the more slender 
rhizomes. It is probably related to increased strength and nutrition of 
the plant. 
An exceptionally rapid transition from a condition with a solid stele to 
the fully adult type is described in what was probably a large well- 
nourished branch. 
10. That the juvenile type of structure is to be regarded as an 
expression in miniature of what is found in full-sized rhizomes, and is to be 
explained on physiological grounds, rather than as a necessary phylogenetic 
recapitulation in the development of the individual, is further shown by 
full-sized rhizomes which become more and more slender. In such cases, 
presumably dependent on poorer nutrition, the stele with adult structure 
assumes in the slender continuation of the rhizome the juvenile size and 
structure. A condensation of structure is shown in such cases, the converse 
of the expansion or elaboration exhibited in the normal ontogeny. 
11. The segmental construction of the rhizome, referred to in the first 
paragraph of the summary, is more or less clearly reflected in the stelar 
anatomy. Corresponding to the ventral segments, a lower, purely cauline 
portion of the stele is recognized. By tracing the tissues towards the apex 
this is confirmed. The stele is regarded as in part at least cauline, and 
not as made up of the united leaf-traces enclosing between them a portion 
of the ground tissue as the pith, as on Campbell’s interpretation. Both the 
segmental construction of the shoot and its morphological unity, as expressed 
in recognizing axis as well as leaves, have to be taken into account. 
11, Comparisons are made with the Zygopterideae and Cycadofilices 
as regards the outer and inner xylems, the secondary thickening, the 
peculiarities of the leaf-trace, and the nature of the branching, and confirm 
the general view of a relationship between the Ophioglossaceae and the 
more primitive Ferns. 
DESCRIPTION OF FIGURES IN PLATES I-III. 
Illustrating Professor Lang’s paper on Hdminthostachys zeylanica. 
(All these figures are from untouched photographs.) 
e., endodermis : e.i., internal endodermis ; ph., phloem; x.o., outer xylem ; x.i., inner xylem; 
px., protoxylem; ad., abaxial portion of xylem of leaf-trace; ad., adaxial portion of xylem of leaf- 
trace ; x. 2 , secondary or accessory xylem. 
PLATE I. 
Photo i. Portion of vascular tube of a rhizome of adult type, showing the well-developed inner 
xylem. x 67. 
E % 
