378 Sahni.—On the Branching of the Zygopteridean Leaf . 
1. The Clepsydroideae (including the genera Clepsydropsis as now 
extended, and Asterochlaena , Corda), and 
2. The Dineuroideae (including Dineuron , Diplolabis , Metaclepsydropsis , 
? Gyropteris , Zygopteris , Etapteris , and Stauropteris), 
The gap between the two lateral xylem-masses of the Stauropterid 
leaf-trace must then be compared to the open peripheral loops of the other 
Dineuroideae. 
IV. Conclusions. 
1. There are in all Zygopterideae, as in all known plants with pinnate 
leaves, only tivo rows of pinnae (secondary raches), one on each side of the 
leaf. The supposed secondary raches of Stauropteris , Metaclepsydropsis , 
Diplolabis , Dineuron , and Etapteris are really tertiary, and the result of the 
forking of the true secondary raches. The latter are completely fused to 
the primary rachis, but their strands are distinct. 
2. This conclusion revives the suggestion (dismissed by Dr. Bertrand as 
improbable) that Gyropteris sinuosa , Goeppert, is a secondary rachis of 
a form like Metaclepsydropsis or Diplolabis , in which this organ acquired 
a cortical sheath independent of the primary rachis. 
3. The mode of branching of the Stauropteris leaf conforms to a 
rectangular system ( idification rectangulaire , P. Bertrand) in which the 
principal plane of each branch-axis is perpendicular to that of its own 
mother-axis. The supposed radial symmetry of the leaf-trace in this genus 
is only superficial. 
4. The laminated portions of the Zygopterid leaf were probably held 
in a more or less horizontal position, with all the segments expanded in the 
same plane, as in the modern Ferns. 
5. Unger’s genus Clepsydropsis (1856) is extended to include the genus 
Ankyropteris , P. Bertrand (1909), and is divided into two sections named 
after the two original genera. 
The Zygopterideae are divided, on the basis of the vascular structure, 
into the two sub-families Clepsydroideae and Dineuroideae, after the names 
of their most primitive genera. In the Clepsydroideae, which are the more 
primitive group, and include the genera Clepsydropsis and Asterochlaena, the 
peripheral loops are permanently closed ; the pinna-trace arises as a closed 
ring, and branches monopodially at the base to supply similarly shaped 
aphlebia-traces. In the Dineuroideae, including the remaining genera of 
Zygopterideae, the peripheral loops open at each pinna-trace exit; the 
pinna-trace is an open arc, and dichotomizes into two equivalent pinnule- 
traces. These may branch monopodially at the base to supply similar 
aphlebia-traces. The relations of the genera are shown in the table (p. 376), 
which is a modification of Dr. Bertrand’s latest scheme. 
It is my pleasant duly to express my heartfelt thanks to Professor 
