KIDSTON : THE FLORA OF THE CARBONIFEROUS PERIOD. 347 
Plate LL, fig. 3 and text fig. 2) and Lepidodendron acuminatum 
Gopp. sp., it is ornamented with irregular transverse lines. 
The fructification consists of cones (Lepidosfrobus), and in the 
great majority of species these terminate the small branches (Plate 
Lll., fig. 2). In a few species, as in Lepidodendron V eltheimianum 
Sternb. (Plate LVIL, fig. 1), the cones are sessile and are borne on the 
large stems in two opposite rows, the cones of one row alternating 
with those of the other row. It is a peculiar and marked character 
of these so-called Ulodendroid Lycopods that the fructification is only 
produced on stems of considerable size and age. When the cones at 
maturity fall from the stem they leave a small cup-like depression, 
which, during the subsequent life of the tree, increases in size as the 
tree increases in girth. 
In many species the cones contain macrospores in the lower 
sporangia and microspores in the upper sporangia, but whether all 
the Lepidodendra possessed heterosporus cones or not, is not yet 
ascertained. 
If a well-developed stem of Lepidodendron showing structure is 
examined, it will be found in most cases to consist of a central pith, 
surrounded by a zone of primary wood, the component elements of 
which are arranged without definite order, and to which when once 
formed no increase takes place. This is succeeded by a zone of 
secondary wood with medullary rays, in which the elements are 
arranged in radial order. Immediately outside is a cambium from 
which additions are made to the secondary wood, by which means its 
extent of increase in width is only limited by the life of the tree. The 
whole is surrounded by a very thick cortex, generally separable into 
three zones, which have been termed the inner, middle, and outer 
cortex. The outer cortex consists of long, tough, fibrous tissue, 
which adds strength and hardness to the outer portion of the bark. 
The leaf-bundles spring from the outer surface of the primary wood 
and passing upwards and outwards enter the leaves. 
Some species have a solid axis and are destitute of a pith, while 
in a few supposed Lepidodendron stems secondary wood has not yet 
been observed, but this may simply be that sufficiently old stems for 
the development of secondary wood in these species have not yet 
been discovered. 
