^] LEAVES OF CALAMITES. 329 



stem, than the bands of xylem tracheids, a. The narrow band, 

 c, consists of four rows of the parenchymatous tissue of a medul- 

 lary ray. At the inner end of each group of tracheids there is 

 a large carinal canal. 



The question of the recognition of the pith-casts of stems 

 possessing the structure of any of the three subgenera of 

 Calamites is referred to in a later section of this chapter. 



h. Leaves. 



Leaves of Calamites and Calamitean foliage-shoots, including 

 an account of (a) Calamocladus (Asterophyllites) and 

 (0) Annularia. 



Our knowledge of the structure and manner of occurrence 

 of Calamite leaves is very incomplete. There are numerous 

 foliage-shoots among the fossils of the Coal-Measures which are 

 no doubt Calamitean, but as they are nearly always found apart 

 from the main branches and stems, it is generally impossible 

 to do more than speak of them as probably the leaf-bearing 

 branches of a Calamite. The familiar fossils known as Astero- 

 phyllites, and in recent years often referred to the genus 

 Calamocladus, are no doubt Calamitean shoots; but they are 

 usually found as isolated fragments, and it is seldom that we 

 are able to refer them to definite forms of Calamites. Another 

 common Coal- Measure genus, Annularia, is also Calamitean, 

 and at least some of the species are no doubt leafy shoots of 

 Calamites. Although it is generally accepted that the fossils 

 referred to as Asterophyllites or Calamocladus are portions of 

 Calamites, and not distinct plants, it is convenient, and indeed 

 necessary, to retain such a term as Calamocladus as a means of 

 recording foliage-shoots, which may possess both a botanical and 

 a geological value. 



Some of the Calamite casts, especially those referred to 

 the subgenus Calamitina, are occasionally found with leaves ' 

 attached to the nodes. In some stems the leaves are arranged 

 in a close verticil, and each leaf has a narrow linear form and 

 is traversed by a single median vein. Figures of Calamite 



