200 kidston: the flora of the carboniferous period. 
III. — Stylocalamites. Here the stems are either unbranched 
or, if lateral branches occur, they 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 Scliimper. 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 (Stylocalamites) Suckoivii 
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 figure of Calamites (Calamitina) approximatus 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 
liave 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 VL, 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, and the whole is enclosed in a thick cortex. 
Modifications of this structure occur in different members of the 
group, but all conform in their outstanding features to this type 
