HORSETAILS 209 



which we usually associate with the Horsetail 

 class. There was, however, one much later Cala- 

 mite (from the Upper Coal Measures) which re- 

 tained the forked leaves of earlier days. 



The cones of Archceocalamites were also re- 

 markable. Instead of whorls of bracts and fertile 

 scales being present in equal numbers, succeed- 

 ing each other alternately throughout the cone, 

 nearly all the whorls consisted of fertile scales, 

 bracts only occurring, if at all, at long intervals. 

 Thus, in this early type, the arrangement was 

 more like that in an ordinary Horsetail than in 

 other Calamites. The fertile scales themselves, 

 however, bore only four sporangia each, and in 

 that respect were Calamitean. There are some 

 other Palaeozoic cones more or less like those of 

 Equisetum, though not very much is known about 

 them at any rate it is clear that in those days 

 there was considerable variety in the fructifica- 

 tions of this group, now so uniform. 



There is a Lower Carboniferous Calamite 

 which is interesting from the structure of the 

 wood. In ordinary Calamites, as in Equisetum, 

 the wood all lies to the outside of the canal accom- 

 panying the vascular strand, and the whole of it 

 was developed from within outwards. In the 

 Lower Carboniferous Protocalamites, there is 

 wood on the inner side of the canal also, and this 

 part was developed from without inwards. This 



