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X. On the Organization of the Fossil Plants of the Coal-Measures. — Part TX. 
By Professor W. C. Williamson, F.R.S. 
Received June 7, — Read November 15, 1877. 
[Plates 19-25.] 
In Part I. of this series of memoirs (Phil. Trans. 1871, Plate 25, fig. 16, and Plate 27, 
fig. 39, p. 487) I described what apjieared to be a transverse section of a Calamite, 
in which the woody wedges showed no traces of the longitudinal canal that occupies 
the innermost angle of each of these primary wedges in true Calamites. Not having 
at that time the materials which I have since accumulated, I was unable to say much 
about this exceptional specimen. I now know that it is not a Calamite, but a plant 
having a wholly different structure, and to which I propose assigning the provisional 
name of Astromyelon, from the peculiar stellate form which transverse sections of its 
pith exhibit. The plant had branching, unarticulated stems, a feature which at once 
distinguishes it from the Calamites, though transverse sections of the two plants 
exhibit such remarkable resemblances. It is one of the more common of the forms 
met with in the Oldham nodules. I have rarely seen specimens of it more than 
0'25'" in diameter. One example alone, represented in fig. 5, has had a diameter of 
nearly 0'7 5. Fig. 1 represents the more usual aspect of transverse sections of this 
plant enlarged 20 diameters. It consists of a central parenchymatous medulla, a, 
surrounded by an exogenous cylinder of vessels arranged in a very regular series of 
primary wedges, b, correspond in g closely in all respects with those of Calamites, 
except hi the absence of the long canals already referred to. The central cells of the 
medulla are much larger than those of the circumference, some of the former having 
a diameter of 'Oil, whilst the peripheral ones are not more than ’0041. In the 
longitudinal section, fig. 2, a, and fig. 3, a', these medullary cells are seen to be 
somewhat elongated vertically, being often - 022 in length. The cells have usually 
rectangular partitions, and are arranged in vertical rows, as in many living ferns ; one 
or two of the rows in immediate contact with the vascular zone (fig. 3, a') have a 
similar arrangement, though they are much narrower in them transverse diameter. 
In the great majority of cases the pith is solid. In but a few instances have I found 
it otherwise. Two of the latter are represented in figs. 4 and 5. Fig. 5 further 
* These measurements are, as in my preceding memoirs, made in parts of an inch, 
MDCCCLXXVIII. 2 T 
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