Sinnott . — The Evolution of the Filicinean Leaf -trace. 183 
Psaronius shows the most complex vascular system of any fern which 
we know. Its stems are large and contain many vascular strands arranged 
in a series of concentric circles, the relation of which to each other and to 
the leaf-trace has only recently been worked out. The trace itself departs 
from the outermost circle as a single broad arch, though this sometimes 
appears to be divided into two separate bands. The whole structure of the 
genus seems clearly not a primitive one, but the result of long development. 
The Botryopterideae, or Inversicatenales of Professor C. E. Bertrand, 
on the other hand, are protostelic and probably much nearer to the original 
condition of affairs in the ferns. Three main families of this order, the 
Zygopterideae, the Anachoropterideae, and the Botryopterideae, are recog- 
nized by Dr. Paul Bertrand (2) in his masterly work on the anatomy of the 
Zygopteridean leaf. In all but the most primitive members of the first 
family the leaf-bundle is of the well-known ‘ H ’ type, more or less modified, 
with four mesarch protoxylem groups ; in the second, it has the shape of 
a C with its convexity towards the stem axis and with two groups of endarch 
Fig. 10 
Fig. 10. The petiolar bundle of Clepsydropsis. Fig. i i . The petiolar bundle of Asterochlaena. 
protoxylem ; and in the last, it is elongated radially, with one or sometimes 
two groups, which are also endarch. 
In the genus Clepsydropsis of Unger, Dr. Bertrand finds a type of 
leaf-bundle which seems very primitive and which is probably ancestral for 
the whole family. It consists of a more or less elliptical body of xylem, at 
either pole of which is completely immersed an island of parenchyma with 
protoxylem at its margin (Text-fig. 10). Dr. Bertrand believes that by the 
disappearance of its centripetal wood and by the lateral and abaxial 
extension of its centrifugal wood, this bundle has given rise to such arched 
types of leaf-stele as are found in Anachoropteris and Tnbicaiilis , and that 
by further reduction these have produced the condition found in Botryo- 
pteris . By its increased constriction and the splitting into two of each proto- 
xylem cluster, the ‘ H ’ type of bundle characteristic of Zygopteris , Eta- 
pteris , Ankyropteris , and Stater op teris has been derived. A rather clear series 
of connecting forms has been established by Dr. Bertrand in all these cases 
and his hypothesis seems well founded. 
It is noteworthy in the light of these researches that a very primitive 
condition of the leaf-bundle was a clearly mesarch one with two protoxylems. 
