200 kidston: tiik flora of tiif, carboxiferous pkriod. 



in. — Stylocalamitks. Here tlie stems are either unbranclied 

 or, if lateral branches occur, tliey are developed very irregularly. 



In all these divisions the ribs on the pith-cast alternate at 

 the nodes. 



There is a fourth division which, however, only occurs in the 

 Lower Carboniferous : — 



IV. - --Asterocalamites Schimper. In these plants the ribs 

 do not alternate at the nodes, and the branch scars are 

 irregularly produced. 



Before considering these groups more fully it is desirable 

 to make a few general remarks on the Calamites as a whole. 



The majority of the fossils referred to Calamites have ribbed 

 exteriors, such as the figures of Calamites ( Stylocalam^ites ) Suckowii 

 given by Brongniart and others (Plate XXXV., fig. 3). These 

 do not represent the exterior of the plant as originally supposed, 

 but are merely the casts of the pith cavity. This is well seen in 

 the figui'e of Calamites (Calamitina) app?-oxim,atus Brongt. given 

 on Plate XXXV., fig. '2, where the cast of the pith cavity is 

 seen at a, and the vascular portion of the stem at b. Plate 

 XXXIV., fig. 2, also shows the same characters. The true 

 outer surface of the stem of Calamites is rarely preserved, and 

 though very young stems may show faint ribs the older stems 

 have almost invariably smooth barks, though on rare occasions 

 a ribbing of the outer surface seems to occur as in some 

 examples of Calamites (Calamitina) verticillatus L. k. H. (Plate 

 XXX VI., fig. 4). 



The stems of Calamites (except possibly in the very young 

 condition) were hollow except at the nodes, where a more or 

 less complete diaphragm of cellular tissue extended across the 

 cavity. The pith cavity was surrounded by a zone of vascular 

 wedges, in the inner angle of which is a carinal canal. This 

 woody zone increased indefinitely in size by additions from a 

 cambium ring. The vascular wedges are separated by broad 

 medullary rays, anfl the whole is enclosed in a thick cortex. 

 Modifications of this structure occur in different members of the 

 group, but all conform in tlieir outstanding features to this type 



