PTERIDOPHYTA. 



1515 



sheaths found at the joints of the stalks, which in an early stage of 

 development consist of a number of leaflets, with median veins, and 

 attached by their margins. In the course of development these 

 sheaths split either into thin component leaflets, or more frequently 

 into two equal and opposite portions (as in the figure), which thus 

 simulate paired leaves. The stems and stalks are longitudinally 

 ribbed. Phyllotheca, which occurs in Europe from the Lias to 

 the Lower Jurassic, in the Lower Gondwanas of India, and the 

 Newcastle beds of Australia, seems to be more nearly allied to 

 Equisetuj?i, but is placed by Schimper in this family. The joints 

 of the stem are of moderate length, and the outer surface is fluted ; 

 while the leaves are linear, and free at their extremities, but at 

 the base are united in a sheathing whorl, which may be longer 

 than the joints of the stem. Each leaf has a midrib. 



With the Calamitece we come to another extinct family, which is 

 confined to the Palaeozoic, and contains the largest representatives 



Fig. 1381. — Restoration of Fig. 1382. — Leaves and branchlets of Calamites ramosus 



Calamites, greatly reduced. {Asterophyllitesfoliosa); from the Carboniferous of England. 



A, C. Suckozvii; B, C. Cistii. Reduced. (After Lindley and Hutton.) 

 (After Dawson.) 



of the class, some of the species probably attaining a height of 

 about 30 feet. Their stems are tall and cylindrical, with a hollow 

 pith-cavity divided into sections by diaphragms, and bearing at 

 the joints either whorls of needle-like leaves (fig. 1381, b), or 

 branchlets carrying secondary whorls of leaves (fig. 1381, a). In 

 transverse section these stems show radiating bundles of fibres, 



