Zygopteris Grayi of Williamson. 65 
In the meantime it seems to me to be established that a somewhat close 
affinity exists between the genera Ankyropteris and Asterochlaena. We 
cannot of course derive one from the other ; Ankyropteris has advanced along 
the line of high differentiation of the petiolar strand, while Asterochlaena 
is distinguished by the complexity of the vascular structure in the stem. 
Summary. 
1. Zygopteris Grayi is a member of the genus Ankyropteris , as shown 
especially by the presence of peripheral loops on the leaf-trace. The 
resemblance of the petiole to Zygopteris (E tap ter is) di-up silon is therefore 
illusory. 
The opinion of Dr. P. Bertrand is thus confirmed. 
2. The protoxylem of the stem is situated in the internal rays of the 
xylem-arms, and passes out thence into the peripheral loops of the leaf- 
trace, which are differentiated before the trace leaves the stele. 
3. The protoxylem of the axillary stele is likewise directly continuous 
with that of the internal rays of the main stele. 
4. The undivided leaf-trace or meristele is, from its base upwards, of 
the nature of a foliar strand and not of a branch-stele. Its structure is, 
however, affected to a varying extent by the presence of the axillary stele. 
5. The branching is rightly described as axillary rather than as dicho- 
tomous. 
6. Internal xylem is always present, both in the main and the axillary 
stele. There is at present no evidence for the existence of a true pith, 
without internal tracheides, in any member of the Zygopterideae. 
7. Aphlebiae occur abundantly both on the stem and the leaf-base. 
Their strands are given off from the leaf-traces both below and above their 
departure from the stele. 
8. The aphlebiae are modified basal pinnae of the leaf, as shown by 
the structure and mode of origin of their vascular strand. The free aphlebia, 
however, contains two or three vascular strands, which are branches of the 
original one. 
9. Ankyropteris , and especially A. Grayi i shows a close affinity with 
the genus Asterochlaena , the latter differing from the former chiefly in the 
presence of more than one series of leaf-traces in connexion with each arm 
of the stele. 
10. The vascular system of Ankyropteris is regarded as probably 
a highly elaborated protostele, rather than as a condensation of a polystelic 
structure. 
For the loan of sections or photographs I am indebted to my friends 
Dr. R. Kidston, F.R.S., Prof. F. E. Weiss, and Dr. P. Bertrand, to whom 
I wish to express my warm thanks. 
F 
