20 
Birbal Sahni. 
study of the corresponding structures in the living Ferns it seems 
more natural and therefore preferable to regard the strand in all 
such cases as being of a dual nature. The relative importance of 
the leaf and branch portions of the strand are subject to variation. 
In the figured Williamson specimens of Zypopteris Grayi the axial 
characters predominate, while in Dr. Scott’s specimen the leaf- 
trace characters are more prominent, though still there is, in the 
latter specimen, a fairly well-developed adaxial bulge with its 
median strand of “ mixed ” internal xylem, destined to supply the 
branch. A similar variation in the relative importance of leaf and 
hranch has been noticed by Professor Bower in Plagiogyria 
(loc. cit „ 1910, p. 434). 
Professor Bower’s account of the branching of Cheiropleuria 
bicuspis 1 is particularly illuminating in connection with this 
question. When the leaf has no branch in connection with it, 
its trace arises as a small tangentially flattened strand which 
divides into two before entering the petiole. When there is a 
branch connected with the leaf, a very much larger circular strand 
is given off from the main stele. Evidently this strand cannot 
correctly be described as the leaf trace, for at the proper level two 
small strands come off from its inner-face, and these constitute the 
divided part of the leaf-trace, while the bulk of the original strand 
passes into the “ infra-axillary ” branch. Since the leaf belongs 
properly to the main axis, the basal undivided portion of its trace 
must be regarded as being adherent to the inner face of the 
ramular portion of the “ undivided trace.” 
The branching of Pterldium aquilinum still remains a puzzling 
case, in spite of the fact that this is such a common Fern, and has 
so frequently been investigated since the time of Hofmeister. No 
completely satisfactory interpretation can be given of the morph¬ 
ology of the vascular system of branch and leaf in this species, 
by any of the views hitherto offered. The more recent observations 
are those of Velenovsky, 2 Bayer, 3 and Mr. Tansley, 4 but only the 
last-mentioned author has taken account of all the different forms 
of branching observed in this species. It appears, however, that 
the only way to arrive at a definite solution, namely, a study of the 
development of the plant, has still to be carried out. 
Mr. Tansley also described in Pteris incisa var. integrifolia, a 
1 Bower, Annals of Botany, 1915, Fig. 7, p. 505. 
* Velenovsky. Sitzungsber. Bohm. Ges. Prag., 1890 (Review in German 
Bot. Centralblatt, Vol. 46, 1891, p. 32), 
3 As referred to in Velenovsky, Vergleichende Morpbologie, 1905, Vol. 1, 
4 Tansley and Lulham. New Phytologist, 1904, p. 1, 
