spirally disposed tubercles, resembling the papillæ at the base of the spines of Echini. From each tubercle there proceeded a cylindrical and probably succulent leaf; these extended to the length of several feet from all sides of the branches. (Pl. 56, Figs. 10. 11.) The leaves, usually, in a compressed state, are found penetrating in all directions into the sandstone or shale which forms the surrounding matrix; they have been traced to the length of three feet, and have been said to be much longer.[1]
In many of the strata that accompany the coal, fragments of these plants occur in vast abundance; they have been long noticed in the sandstone called Gannister and Crow-stone, in the Yorkshire and Derbyshire coal fields, and have been incorrectly considered to be fragments of the stems of Cacti.
The discovery of the dome-shaped centres above described,
and the length and forms of the leaves and branches
render it highly probable that the Stigmariæ were aquatic
plants, trailing in swamps, or floating in still and shallow
lakes, like the modern Stratiotes and Isoetes. From such
situations they may have been drilled by the same inundations,
that transported the Ferns and other land vegetables,
with which they are associated in the coal formation. The
form of the trunk and branches shows that they could not
have risen upwards into the air; they must therefore either
have trailed on the ground, or have floated in water.[2] The
sion there is found a loose internal eccentric axis, or woody core, (Pl. 56. Fig. 10. a.) surrounded with vascular fasciculi that communicated with the external tubercles, and resembled the internal axis within the stems of certain species of Cactus.
- ↑ All these are conditions, which a Plant habitually floating with the leaves distended in every direction, would not cease to maintain, when drifted to the bottom of an Estuary, and there gradually surrounded by sediments of mud and silt.
- ↑ The place and form of the leaves, supposing them to have grown on all sides of branches suspended horizontally in water, would have been but little changed by being drilled into, and sinking to the bottom of, an
