58 STUDIES IN FOSSIL BOTANY 



this process, going on more freely in some sporangia 

 than in others, may ultimately have rendered possible 

 the excessive development of those spores that survived, 

 at the expense of the others, and may thus have led to 

 the development of specialised megaspores. 



In the heterosporous species, Calamostachys Casheana, 

 the axis of the cone formed a zone of secondary wood, 

 precisely as in the homosporous form, C. Binneyana, 

 shown in Fig. 19. This fact is of considerable signi- 

 ficance, in view of the excessive importance which 

 palaeobotanists have sometimes attached to secondary 

 growth, as an indication of Phanerogamic affinities. 



We have next to consider the relation of Calamo- 

 stachys to Calamites. Neither of the British species 

 described has as yet been found in connection with the 

 stem or with vegetative organs of any kind. On the 

 other hand, very similar Continental species have been 

 found with such connection. In the Calamostachys 

 Ludivigi of Carruthers, 1 for example, from the German 

 Coal-measures, the spikes are borne upon a ribbed stem 

 with whorled leaves, agreeing exactly with the smaller 

 Calamitean twigs. In this species the structure of the 

 cone is perfectly well known ; it is that characteristic 

 of the British forms of Calamostachys, except that in 

 C. Ludwigi the bracts of the cone are free, instead of 

 being coherent. This fossil thus affords certain evidence 

 that fructifications of the Calamostachys type were borne 

 on Calamitean stems, 2 a fact fully recognised by Mr. 

 Carruthers, in his memoir of 1867, just cited. 



1 Carruthers, "On the Structure of the Fruit of Calamites" Seemann's 

 Journal of Botany, vol. v. 1867. At that time the generic name Volk- 



mannia was used for Calamarian strobili. 



2 See Weiss, Sleinkohlen- Calamarien, ii. p. 163; Atlas, IMates 



