166 HISTORICAL PALASONTOLOGY. 
in the Carboniferous deposits, and have given occasion to an 
abundance of research and speculation. ‘They present them- 
selves as prostrate and flattened striated stems, or as similar 
uncompressed stems growing in an erect position, and some- 
times attaining a length of twenty feet or more. Externally, the 
stems are longitudinally ribbed, with transverse joints at regular 
intervals, these joints giving origin to a whorl of branchlets, 
which may or may not give origin to similar whorls of smaller 
branchlets still. The stems, farther, were hollow; with trans- 
verse partitions at the joints, and having neither true wood nor 
bark, but only a thin external fibrous shell. There can be little 
doubt but that the Ca/amites are properly regarded as colossal 
representatives of the little Horse-tails (Zgzcsetacee) of the 
present day. They agree with these not only in the general 
details of their organisation, but also in the fact that the fruit 
was a species of cone, bearing ‘‘spore-cases”’ under scales. 
According to Principal Dawson, the Calamites ‘ grew in dense 
brakes on the sandy and muddy flats, subject to inundation, 
or perhaps even in water ; and they had the power of budding 
qut from the base of the stem, so as to form clumps of plants, 
and also of securing their foothold by numerous cord-like roots 
proceeding from various heights on the lower part of the 
Stem.” 
The Lepidodendroids, represented mainly by the genus 
Lepidodendron itself (fig. 110), were large tree-like plants, 
which attain their maximum in the Carboniferous period, but 
which appear to commence in the Upper Silurian, are well 
represented in the Devonian, and survive in a diminished form 
into the Permian. The trunks of the larger species of Lepzdo- 
dendron at times reach a length of fifty feet and upwards, giv- 
ing off branches in a regular bifurcating manner. The bark 
is marked with numerous rhombic or oval scars, arranged in 
quincunx order, and indicating the points where the long, 
needle-shaped leaves were formerly attached. The fruit con- 
sisted of cones or spikes, carried at the ends of the branches, 
and consisting of a central axis surrounded by overlapping 
scales, each of which supports a ‘‘spore-case” or seed-vessel. 
These cones have commonly been described under the name 
of Lepidostrobi. In the structure of the trunk there is nothing 
comparable to what is found in existing trees, there being 
a thick bark surrounding a zone principally composed of 
“scalariform” vessels, this in turn enclosing a large central pith. 
In their general appearance the Lefidodendra bring to mind 
the existing Araucarian Pines; but they are true “Crypto- 
gams,’’ and are to be regarded as a gigantic extinct type of the 
