214 The Palaeontological Record. II. Plants 
the collective name Primofilices); the best known of these are 
referred to the family Botryopterideae, consisting of plants of small 
or moderate dimensions, with, on the whole, a simple anatomical 
structure, in certain cases actually simpler than that of any recent 
Ferns. On the other hand the sporangia of these plants were usually 
borne on special fertile fronds, a mark of rather high differentiation. 
This group goes back to the Devonian and includes some of the 
earliest types of Fern with which we are acquainted. It is probable 
that the Primofilices (though not the particular family Botryopte- 
rideae) represent the stock from which the various families of modern 
. Ferns, already developed in the Mesozoic period, may have sprung. 
None of the early Ferns show any clear approach to other classes 
of Vascular Cryptogams; so far as the fossil record affords any 
evidence, Ferns have always been plants with relatively large and ~ 
usually compound leaves. There is no indication of their derivation 
from a microphyllous ancestry, though, as we shall see, there is some 
slight evidence for the converse hypothesis. Whatever the origin of 
the Ferns may have been it is hidden in the older rocks. 
It has, however, been held that certain other Cryptogamic phyla 
had a common origin with the Ferns. The Equisetales are at present 
a well-defined group; even in the rich Palaeozoic floras the habit, 
anatomy and reproductive characters usually render the members of 
this class unmistakable, in spite of the great development and stature 
which they then attained. It is interesting, however, to find that in 
the oldest known representatives of the Equisetales the leaves were 
highly developed and dichotomously divided, thus differing greatly 
from the mere scale-leaves of the recent Horsetails, or even from the 
simple linear leaves of the later Calamites. The early members of 
the class, in their forked leaves, and in anatomical characters, show 
an approximation to the Sphenophyllales, which are chiefly repre- 
sented by the large genus Sphenophyllum, ranging through the 
Palaeozoic from the Middle Devonian onwards. These were plants 
with rather slender, ribbed stems, bearing whorls of wedge-shaped 
or deeply forked leaves, six being the typical number in each whorl. 
From their weak habit it has been conjectured, with much proba- 
bility, that they may have been climbing plants, like the scrambling 
Bedstraws of our hedgerows. The anatomy of the stem is simple and 
root-like ; the cones are remarkable for the fact that each scale or 
sporophyll is a double structure, consisting of a lower, usually sterile 
lobe and one or more upper lobes bearing the sporangia; in one 
, species both parts of the sporophyll were fertile. Sphenophyllum 
was evidently much specialised ; the only other known genus is based 
on an isolated cone, Cheirostrobus, of Lower Carboniferous age, with 
an extraordinarily complex structure. In this genus especially, but 
