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 



