OF THE FOSSIL PLANTS OF THE COAL-MEASURES.—PART XIII. 
297 
enlarged 39 diameters; its vascular bundle is shown, enlarged 187 diameters, in 
tig. 33a. This example closely resembles a triarch rootlet-bundle. Plate 24, fig. 34, 
is yet smaller, also from Oldham, and enlarged 39 diameters. Its bundle, e, enlarged 
187 diameters, is represented in fig. 34a. It now consists of but six vessels. Figs. 35, 
36, and 37 are three sections of these root-like structures from Oldham, becoming 
successively smaller, so that in fig. 37 the epidermal layer, p", now consists only of a 
single layer of cells enclosing but a very small number of cortical ones. The vascular 
bundle of fig. 35, seen at fig. 35a, is now distinguished with difficulty from the cells 
by which it is surrounded. So far as I can determine, it consists of the five vessels 
marked e, e. In like manner, the bundle of fig. 36, represented at fig. 36a, seems to 
consist of the three vessels marked e, e ; whilst that of fig. 37, shown at fig. 37a, 
seems to consist of the two vessels indicated by the same letters. All the Oldham 
specimens just described, viz., figs. 28, 29, 33, 34, 35, 36, and 37, belong to one great 
cluster of root-like examples crowded together in one slide; amongst them are other, 
more completely developed specimens, showing that the entire series belongs to 
Kaloxylon Hookeri. My first impression was that the whole cluster consisted of a 
series of rootlets, and the study of such examples as figs. 30, 31, and 32 not only 
seemed to confirm this opinion, but to show that they were rootlets with a tetrarch 
development of their several primary xylem bundles. But on tracing the development 
of those bundles downwards through such examples as figs. 34, 35, 36, 37, it became 
evident that, if the objects of which they formed a part were rootlets, the bundles had 
not been developed centripetally in the way characteristic of living rootlet-bundles, 
and which also was the case with other plants (e.g., Stigmaria Ficoides ) that lived 
during the Carboniferous age. Nevertheless, it is difficult to believe that these organs 
have been other than roots; though the apparently centrifugal growth of their 
bundles is more suggestive of an axial cauline development than of radicular 
structures. # 
We may now ask : Can any light be thrown upon the systematic affinities of the 
two plants, Heterangium Tiliceoides and Kcdoxijlon Hookeri, described in the preceding 
* [I find amongst the Carboniferous plants other examples of what appear to be branching stems, 
which diminish gradually in diameter, until, as in the instance described in the text, they become 
extremely slender. At the same time that they are reduced in size, they rapidly increase in the number 
of the transverse sections of them that are met with in our slides. The Bachiopteris Oldhamium, 
described in my Memoir, Part YI. (‘Phil. Trans.,’ Part 2, 1874), presents these conditions. The figures 
20-24 on Plate 53 of that memoir show a gradation of diameters of sections from about 425 to '006 
of an inch ; yet none of these sections display the slightest trace of any foliar appendages. Stems thus 
gradually diminishing in diameter, whilst their numbers are multiplied, must be reduced either to the 
condition of aerial twigs or of subdividing roots and rootlets. If the former, where are their foliar 
appendages ? If the latter, why do not their fibro-vascular bundles show the symmetrical arrangement 
telling of the centripetal development so characteristic of the proto-xylems of all roots F Of coui’se the 
idea suggests itself that these curious objects may have had some relationships wdth the rootless sub¬ 
terranean branches of Psilottcm , though many difficulties interfere with our ready acceptance of this 
explanation.—August 12th, 1887.] 
MDCCCLXXXVII.-13. 2 Q 
