408 SPHENOPHYLLALES. B. PSILOTACEAE 
of Sphenophyllum in which the arrangement of the sporangia is in a group 
disposed radially around a central attachment—a condition comparable 
with that of the Calamarians, and which was 
st probably a relatively primitive state. Finding these 
st st two features combined in the same plant gives to 
both additional weight. But they are also combined 
$ 5 $ in that other series which, following the suggestion of 
Thomas, are here included with the Sphenophyllales, 
viz. the Psilotaceae. These will now be described, 
and the general discussion of the morphology of the 
sporangiophoric Pteridophytes will be reserved till it 
can be illuminated by the facts which these living 
genera supply. 
B. PSILOTACEAE. 
re The genera Zmesipteris and Pstlotum are the only 
Jiavram of the vascular ens - Hf . 
supply to the sterile lobes living representatives of this peculiar and somewhat 
(s7), and to the sporangio- 3 4 ‘ F a 
phores (/) in Cherrostroius. isolated family, while there is nothing known among 
Fossils which can with any certainty be ascribed to 
it. They have commonly been classed with the Lycopodiales, and, as 
we shall see, there are many undoubted points of resemblance in that 
Calamostachys Binneyana. Transverse section of axis of cone, showing stele and part 
of cortex. Surrounding the pith there are six bundles, in groups of two, with secondary 
wood. £.=protoxylem groups. xabout 60. PAr/. Trans. Wo and 8S. Will. Coll., 1016. 
(From Scott's Stwdies in Fossil Botany.) 
direction. But increasing knowledge of the Sphenophylleae, as well as 
of the Psilotaceae themselves, has indicated a more natural position of 
both together in the phylum of the Sphenophyllales. The two genera of 
the Psilotaceae are so similar in their general characters that there is no 
doubt of their close affinity: on the other hand the differences of detail 
