MESOZOIC EQUISETALES 83 



survivors of the Calamites appear to have died out 

 in the Permian at the close of the Primary period. 

 The Equisetineae, however, were well represented during 

 the Secondary epoch, 1 by forms in some respects inter- 

 mediate between the Palaeozoic Calamites and the 

 recent Horsetails. In the Trias very large Horsetails 

 are found, the stem of one of them, Equisetites arenaceus, 

 even attaining a diameter of 20 cm. (8 inches). All 

 parts of this plant — rhizome, aerial stem, leaf-sheaths, 

 and cones — are preserved, and though all the organs 

 are not in connection, there seems no reason to 

 doubt that they really belonged to the same species. 

 In all respects there is a close agreement with our 

 recent Horsetails, but the Triassic plant was on an 

 immensely greater scale ; it had, for example, as many 

 as 120 leaves in a whorl. It is probable that these 

 great stems, like those of the still larger Palaeozoic 

 forms, possessed secondary tissues, but at present this 

 is only a conjecture. In the Rhaetic and Liassic 

 Equisetites of Sweden M. Halle finds that the inter- 

 nodal bundles are three to four times as numerous as the 

 leaf-teeth of a whorl ; the bundles must therefore have 

 traversed at least three internodes. In Neocalamites, 

 a genus separated by M. Halle from Schizoneura (see 

 below), the bundles passed through two internodes, 

 apparently branching in some cases. These facts offer 

 interesting analogies with the Palaeozoic Calamites (see 

 above, p. 26). Numerous Mesozoic species are known ; 

 on the whole their dimensions diminish as the later 

 horizons are approached. Some of the fossil forms, as, 



1 For a fuller account of the Mesozoic Equisetales, see Seward's Fossil 

 Plants, vol. i. 



