BRITISH CARBONIFEROUS PLANTS 137 



by Jeffrey (24). Miss Stopes (61) has described the formation 

 of callus wood in wounded Calamite stems. In her specimens 

 the wounds extended to the pith, and strands of new wood 

 with inverted orientation had been formed to complete the 

 broken xylem ring. 



Further work is desired on this group in the direction of 

 a correlation of the various types of pith casts, so well known 

 as impressions, with structure specimens. 



Sphenophyllales 



The outstanding recent contribution to our knowledge of this 

 group is the description by Scott (46) of the new cone Spheno- 

 phyllum fertile. Here both the dorsal and ventral lobes of 

 the sporophylls are fertile, and " are divided in a palmate 

 manner into several branches each of which constitutes a 

 sporangiophore." This cone is regarded by Scott as a 

 "specially modified rather than a primitive form of fructification." 



A " suggestion of heterospory " in another cone, Spheno- 

 phyllum Daivsoni, has been recorded by Thoday (64) but 

 otherwise this group has not been investigated recently. 

 Further studies of the roots, the mode of branching, and the 

 structure of the leaves remain for the future. 



Lycopodiales 



In quite recent times the lion's share of attention has been 

 devoted to the Palaeozoic Lycopods. Not only has a further 

 seed-bearing Lycopod been described but the correlation of 

 the internal structure of two species of Lepidodendron with 

 their external features has been effected. The structure of 

 the genus Sigillaria has been investigated in several cases, 

 though the full account of the structure of Bothrodendron, 

 discovered some years ago by Lomax, has not yet appeared. 

 Speaking generally, our knowledge of nearly all the great 

 Lycopod genera of Palaeozoic times has been considerably 

 extended, especially anatomically. 



One of the most interesting of recent memoirs has been that 

 by Miss Benson (13) on Miadesmia, the first herbaceous Carboni- 

 ferous Lycopod, which has been made known from structure 

 specimens. This plant bore seed-like organs (integumented 

 megasporangia) with which may be compared Lepidocarpon, 



