Salmi.—On the Branching of the Zygopteridean Leaf. 371 
as far back as 1874, when Williamson ( 19 ) wrote as follows in reference to 
the branching of the vascular axis of Rachiopteris (M.) duplex'. ‘1 know of 
no recent fern in which the secondary branches [meaning pinnae] of the 
petiole are thus given off in pairs, which pairs are distichously arranged on 
the primary axis, and each of which secondary petioles sustains ternary 
ones arranged distichously. Not only will a similar case come before us on 
a later page of this Memoir, in Corda’s genus Zygopteris , but the structure 
of the Rachiopteris oldhamia just described suggests the possibility that 
a somewhat similar arrangement may have existed in its case.’ Stenzel, 
writing in 1889 ( 17 ), divided the genus Zygopteris into two main sections 
(Zygopteris proper and Ankyropteris) according to the biseriate or quadri- 
seriate arrangement of branches which he erroneously regarded as being all 
secondary raches. Solms-Laubach ( 15 ), while justly criticizing Stenzel’s 
classification as being inconsistent on other grounds, passes over the first 
error unnoticed. Finally, Dr. Bertrand ( 2 ), throughout his 1912 paper in 
the ‘ Progressus does not depart in this respect from the position he adopted 
in 1909, except that on p. 221 he suggests that the presence of four rows of 
appendages in Diplolabis is due to a precocious dichotomy ( dichotomie 
hdtive) of the secondary petioles. After this statement he continues to 
regard the products of the dichotomy as secondary raches. 
There are thus in the Zygopterideae , as in all known vascular plants 
with pinnate leaves , only tzvo rows of 'pinnae ’ {secondary raches), one on each 
side of the leaf and the supposed radial symmetry of the Stauropterid leaf- 
trace is purely superficial. In some Zygopterideae, however (. Diplolabis , &c.), 
the whole of the secondary rachis is fused with the primary rachis, though 
the vascular strands of the two are distinct, while the tertiary raches, formed 
by a dichotomy of the tip of the primary rachis, are free (Fig. 1). Each 
tertiary rachis then branches monopodially , giving off small strands which 
supply reduced lateral axes (aphlebiae), which may branch in their turn. 
The monopodial branching of the tertiary raches is thus clearly seen to be 
a reduced form of the dichotomous branching of the secondary raches. In 
other Zygopterideae {Ankyropteris) the secondary raches become free, and 
branch monopodially to give rise to reduced axes (aphlebiae). 
The Zygopterideae (with the sole exception of Stauropteris , according 
to Dr. Bertrand) are generally considered to be peculiar also on account of 
the leaf always branching in a rectangular system {edification rectangulaire , 
Bertrand), the principal plane of each branch-axis being perpendicular to 
that of its own mother-axis. The leaves of Stauropteris and of all the 
higher Ferns, Gymnosperms, and Angiosperms are supposed by Bertrand 
to branch in a parallel system {Edification parallele), so that the branches of 
all orders face in the same direction. 
very similarly shaped leaf-traces, lacking the peculiar horn-like outgrowths of the antennae 
characteristic of Etapteris. 
