On the Branching of the Zygopteridean Leaf, and its 
Relation to the probable ‘Pinna’ Nature of Gyropteris 
sinuosa, Goeppert. 
BY 
BIRBAL SAHNI, B.A. (Cantab), M.Sc. (Lond.), 
Research Student y Emmanuel College , Cambridge. 
With three Figures in the Text. 
I. The Branching of the Zygopteridean Leaf. 
I N 1909 Dr. Paul Bertrand ( 1 ) published an exhaustive comparative 
account of the Zygopteridean leaf, exhibiting m great detail the com¬ 
plex forms assumed by the vascular strands. A special feature of the 
work was the attention paid to the branching of the vascular axis of the leaf, 
to supply the secondary and tertiary axes (‘pinnae’ and ‘pinnules’). 
Where possible the further branching of the tertiary axes was also described, 
and the vascular supply to the aphlebiae was traced. 
It was Dr. Bertrand’s detailed account of Stauropteris oldhamia which 
allowed the structure of this till then rather puzzling species to be interpreted 
in terms of the typical Zygopterid leaf-trace. Assuming that the largest 
axis known is the primary rachis, it is described as bearing altogether four 
series of pinnae (secondary raches), in pairs alternating on the right and 
left sides of the leaf. The vascular supply to these branches is as follows: 
From the cruciate xylem-mass of the primary rachis (Fig. a, D) a single 
large strand, elongated in the antero-posterior plane, becomes detached 
laterally. This is the piece sortante of Bertrand. It never appears to 
acquire a cortical sheath of its own, for it at once divides, symmetrically 
along the right and left plane, into two halves, the demi-pieces sortantes of 
Bertrand. Each of these is described as entering one of the two so-called 
‘pinnae’ (secondary raches) on that side. 1 
If the branching primary axis of Stauropteris were viewed superficially, 
without regard to the vascular anatomy, it would be perfectly natural to 
regard the lateral axes as ‘ secondary ’ raches. But in the presence of the 
single embedded strand ( piece sortante ) which comes off from the side of the 
primary petiolar strand, and which by subsequent division gives rise to the 
1 These latter in their turn branch in an almost identical fashion, and the process is repeated in 
several generations of axes; but we need not follow this in detail. 
fAnnals of Botany, Vol. XXXII. No. CXXVII. July, 1918.] 
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