PTERIDOPHYTA. 



1517 



A large number of synonyms in addition to those already men- 

 tioned have been made ; among which it may be observed that 

 Mr Kidston includes Asterophyllum, or Asterophyllites, and Archceo- 

 calamites in Asterocalamites ; while Calamoden- 

 dron is regarded as inseparable from the type 

 genus. Calamitece occur both in Europe and 

 North America, but are unknown in India and 

 Australia. 



According to Sir J. W. Dawson, "it would seem, 

 from the manner in which dense brakes of these 

 Calamites have been preserved in the coal-forma- 

 tion of Nova Scotia, that they spread over low 

 swampy flats, and formed fringes on the seaward 

 side of the great Sigillaria forest. In this way they 

 no doubt contributed to prevent the invasion of the 

 areas of coal accumulation by the muddy waters of 

 inundations, and thus, though they may not have 

 furnished much of the material of coal, they no 

 doubt contributed to its purity." 



Here may be noticed the remarkable jointed 

 stem-like bodies known as Vertebraria, which 

 are generally regarded as Equisetaceous, and 

 occur throughout the Lower Gondwanas of 

 India, and are also found in the Newcastle beds 

 of Australia. These peculiar bodies, which are 

 often branched, and may be of considerable size, are regarded as 

 the rhizomes of an Equisetaceous plant of which the foliage is 

 unknown. Their association in India with Schizoneura is note- 

 worthy. 



Class III. Lycopodiace^e. — The third and last class of the 

 Pteridophytes, known as Lycopodiacese or Dichotomese, is now 

 represented by the Club-mosses and Selaginellas, and also includes 

 a number of allied extinct types of much larger dimensions. These 

 plants are characterised by a simple or branched stem, without joints, 

 usually having roots, and bearing numerous small and simple leaves ; 

 while the branches of the stem and frequently of the roots divide 

 dichotomously (fig. 1387). The sporangia are solitary, and borne 

 either upon the upper surface of the base of the leaves, or in the 

 axils of the latter, or simply upon the stem. The class may be 

 divided into two orders. 



Order i. Isospore/e. — The Club-mosses, which are the existing 

 representatives of this order, are characterised by producing only 

 one kind of spores, and by the absence of lignlcE, or membranes at 

 the base of the leaves, as well as by certain other points which 

 need no mention here. 



The earliest plant referred to this order is Psilophyton, which is 



Fig. 1384. — Lower ex- 

 tremity of stem of 

 Calamites canncrformis ; 

 from the European Car- 

 boniferous. Reduced. 



