6 
Birbal Sahni. 
this view to all cases discussed in this paper, in which a branch 
arises in close vascular connexion with a leaf. In accordance with 
this view the plane of section in Fig. 1, A, B, D, E must be supposed 
to have passed, at the base of the branch, longitudinally through the 
ramular portion of this composite trace, the foliar portion of the 
latter being proximal or distal to the plane of section according as 
the branch is adaxial (Hymenophyllaceae, Zygopteris, Plagiogyria t 
Botrychium) or abaxial to the leaf ( Cibotium, Lophosoria, Metaxya, 
Cheiropleuria). 
In the protostelic forms the branch always receives, as would 
be expected, a single solid strand which usually remains protostelic 
throughout its length (Hymenophyllaceae , 1 Zygopteris, Cheiropleuria, 
Fig. 1, A). The branching may be either distinctly lateral, as in 
Cheiropleuria and the Hymenophyllaceae, or a forking of the axis, as 
in Zygopteris (Aukyropteris) corrugata , J Diplolahis Rcemeri, Meta- 
clepsydropsis duplex, 3 Botrychioxylon paradoxumS 
In the solenostelic forms we find that the vascular system of 
the branch frequently appears to arise as a diverticulum of an 
associated leaf-trace, ( Lophosoria , Metaxya) but, as explained above, 
may be regarded as being fused along one side of the base of the 
latter. In a number of solenostelic forms investigated by Gwynne- 
Vaughan, the branch at its base has a gutter-shaped strand, which, 
however, rapidly closes up into a complete cylinder (several species 
of Hypolepis, Poly podium punctatum, Dicksonia adiantoides). In the 
Marsiliaceae with a tubular stele in the main axis the branch receives 
also a tubular strand, the pith of the branch being continuous 
through a gap with that of the main axis . 5 According to Professor 
Seward , 6 in Matonia pectinata the rhizome divides by forking, and 
sends into each branch a solenostele, as well as a portion of the 
accessory medullary system. 
The branching of Helminthostachys has recently been described 
in detail by Professor Lang (loc. cit. 1915), and although the plant 
does not possess a typical solenostele it may be considered here. 
The branches arise from dormant axillary buds which are stimulated 
* See, however, p. 14 below, in reference to Hymenophyllum lineare. 
1 Scott, Studies in Fossil Botany, 1908, p. 318. 
s Gordon, Trans. Roy. Soc. Edinb., Vol. XLVII, Part IV, p. 720 and Vnl 
XLVIII, Part I, p. 173. F 01 - 
* Scott, Trans. Linn. Soc., 2nd ser. Botany, Vol. VII, Part XVII, 1912 
p. 383. 
1 De Bary, Comparative Anatomy, English Translation, 1884. p. 313 . 
* Seward, Phil. Trans., 1899, Vol. CXCI, p. 187, 
