162 D. H. Scott. 



of a smaller original number. On the whole the agreement in the 

 vegetative organs of the two classes appears sufficientlj' close to be 

 indicative of real affinity. The difference in the structure of the stele 

 is undoubtedly great, but. as we have seen, there are some indications 

 of intermediate forms. 



When we come to the fructifications the agreement is more striking. 

 The detailed structure of the sporangia is very similar throughout 

 the two groups, and the resemblance extends to the sporangiophores, 

 which in the case of Cheirostrohiis, in particular, are practically iden- 

 tical with those of Calamostachys ; in the bisporangiate Sphenophyllales 

 the agreement is still evident, though it is naturally diminished in 

 the Sphenoplujllum Daivsoni type, where the sporangiophore has only 

 a single sporangium to carry. 



Throughout the Sphenophyllales the sporangiophores appear as 

 ventral lobes of the sporophyll, while in one species the dorsal lobes 

 are also enlisted for the same service. As we have seen above, there 

 is anatomical evidence that in Calamostachya and Palaeostackija the 

 sporangiophores are the more or less displaced ventral appendages of 

 the bracts next below them on the axis. The Equisetum type of strobilus 

 (already represented in the Palaeozoic flora) appears to present diffi- 

 culties, but they are not insuperable. In Sinlienophyllnm fertile both 

 dorsal and ventral lobes of the sporophyll are fertile, and if the same 

 displacement took place under these conditions as we actually find 

 in Calamostachys there would be a near approach to the Equisetum 

 arrangement. Other explanations have been suggested, but need not 

 be discussed here. 



Taking all the characters, vegetative and reproductive, into ac- 

 count, the affinity of the E(iuisetales with the wholly Palaeozoic group 

 Sphenophyllales may be regarded as established. 



It has been proposed (Potonié, 1897 and 1900) to found a group 

 Protocalamariaceae to include Archaeocalamites, Cheirostrohiis and pro- 

 bably Pseiidobornia , the proposed group occupying an intermediate 

 place between Sphenophyllales and ( 'alamariaceae proper. While the 

 general idea of the relationships underlying this suggestion is quite 

 in accordance with the views expressed above, the types included 

 under Protocalamariaceae seem too heterogenous to be usefully asso- 

 ciated in a special class. Archaeocalamites, though it shows some 

 approach to the Sphenophyllales, is none the less a manifest Cala- 

 marian, while in Cheirostrohus the Sphenophyllaceous characters as 

 evidently predominate. Pseiidobornia is probably, in the present state 

 of our knowledge, best kept in a distinct class, as Nathorst proposes 

 though perhaps it has the strongest claims of any known genus to 

 be called a Protocalamarian. 



