156 D- H. Scott. 



discovery is of the greatest interest, and we may hope that our 

 knowledge of this ancient group of plants may eventually be in- 

 creased by the discovery of specimens showing structure. 



II. Equisetales. 



The Palaeozoic Equisetales, often made into a class of their 

 own, under the name Calamariales or Calamariaceae, were one of 

 the dominant groups of plants at that period, attaining the stature 

 of large trees, which appear to have formed an important consti- 

 tuent of the Carboniferous forests. Hence their organization was 

 in various respects on a higher level than that of their recent 

 survivors, represented by the genus Eqtiisetum; at the same time, 

 allowing for these adaptive differences, the structure of the Calama- 

 riaceae had so much in common with that of our familiar Equisetaceae 

 that no very detailed description, except perhaps as regards the 

 fructifications, is necessary for our present purpose. 



Even in habit there seems to have been a considerable resem- 

 blance to recent forms. The leaves were always in whorls, and 

 usually of simple form and comparatively' small size, though not so 

 reduced as in Ecjuisetum itself. In the oldest known Calamarian, 

 however, the Devonian and Lower Carboniferous genus Archaeocalamites, 

 the leaves were often dichotomously compound, tlius showing an 

 interesting analogy with the foliage of Fseudobornia and the Spheno- 

 phyllales. In a later genus, the AutophylUtes of Grand'Eury. dicho- 

 tomous leaves have also been observed. In various Calamariaceae 

 there is evidence that the leaves of a verticil were connate at the 

 base, forming a sheath, though the free laminae were probably always 

 more developed than in the recent family, and generally of a linear 

 or lanceolate form. The leafy branches have been divided among the 

 genera Anmilaria, Asterophjllites and CaJamodadus , but it is not 

 necessary to enter into their distinctive characters here. The stems 

 were always more or less branched, and a number of genera or sub- 

 genera have been founded on characters derived from the distribution 

 of the branches on the main axis. Structural specimens show that, 

 as in the recent genus, each branch was commonly inserted between 

 two leaves, and slightly above the node. In many Calamités there 

 is evidence that the aerial stem sprang from a horizontal rhizome, 

 while in other cases it is found with an independent, rooting base. 



The anatomical structure of all parts of the plant is now known 

 in a number of instances, but the correlation of the various organs 

 in their different states of preservation still presents great difficulties. 



