586 MOSSES' AND FERNS CHAP. 



tially the same. The general points of difference are the com- 

 pletely separate leaves of the Calamites, the frequent absence of 

 diaphragms at the nodes, and the marked secondary thickening 

 of the vascular bundles. Cormack has shown that a slight 

 thickening of the same character occurs in the nodes of Equi- 

 setuni maximum, and in the Calamites this thickening seems to 

 begin in the nodes and to extend later to the internodes. He 

 concludes that all the Calamites possessed this secondary thick- 

 ening of the stem. The two groups Annularieae and Aster- 

 ophylliteae, which have slender stems with regular whorls of 

 leaves at the nodes, have been found to be to some extent, at 

 least the smaller branches, of indubitable Calamitese; but it is 

 questionable whether this is always so. 



The most important remains of this group are the fossils 

 known under the name Calamostachys. These are cone-shaped 

 structures, whose close affinity with Equisctum is beyond ques- 

 tion. The whorls of sporophylls, which are peltate, like those 

 of Equisctum, and bear four sporangia upon the lower surfaces, 

 are separated by alternating whorls of sterile leaves. Through 

 the kindness of Dr. D. H. Scott I have had an opportunity of 

 examining a beautiful series of sections of C. Binneyana. The 

 structure of the axis and sporangia correspond in the closest 

 manner to those of Equisctum, but a most interesting difference 

 is the fact that this genus- was heterosporous. Macrospo- 

 rangia and microsporangia occurred in the same strobilus, but 

 the difference in the size of the spores is much less than in the 

 living heterosporous Ferns and Lycopods. 



The oldest known fossil belonging to the Equisetineae is 

 Asterocalamitcs (Archccocalamitcs) , which has been made the 

 type of a special family Protocalamariacere. Astcrocalamites 

 was structurally very much like Equisctum, from which it dif- 

 fered, however, in the leaves, which were much better devel- 

 oped, and not united into a sheath. The leaves were repeat- 

 edly forked, and of considerable size (Scott ( i), Figs. 28, 29). 

 The cones are not certainly known, but a cone quite similar to 

 that of Equisctum has been found which perhaps belongs to 

 Asterocalamites, and has been attributed to that genus. 



The name Equisctitcs has been given to those fossil Equise- 

 tacese which closely resemble the living genus Equisctum. In 

 the Triassic and Jurassic were numerous arborescent Equise- 

 taceae which closely resembled the living genus Equisctum, but 



