900 PROFESSOR W. CU. WILLIAMSON AND DR. D. H. SCOTT ON THE 
Astromyelon was founded identical with the Calamitean appendages of M. RENAULTS 
collection ? 
We propose to reserve the detailed consideration of Astromyelon for another 
occasion, but a preliminary examination of the slides in the Witt1amson Collection 
shows that the larger specimens, at any rate, namely those with a distinct pith,* have 
the same structure as M. Renavurt’s specimens, which are directly borne on a 
Calamitean stem. The question as to the identity of «ll the forms grouped under 
Astromyelon in a former memoir,t will have to be reconsidered in the new light which 
has now been thrown on these fossils. It is, however, highly probable that we 
possess, in the various forms of Astromyelon, not merely the principal roots, but also 
the finer rootlets of Calamites. 
It is interesting to recall the fact that the first specimens of Astromyclon were 
originally described under the name of Calamites,{ but subsequently separated, on the 
ground of certain structural differences which find a sufficient explanation, if the 
organs in question are to be regarded as roots and not stems.§ 
We still require much further information respecting the earliest stages of the 
development of Calamites, in order to fill up the gap between two states, as to which 
we already possess considerable knowledge. We now know the spores of Calamutes 
pedunculatus|| which we may regard as a typical fructification of the Arthropitoid 
Calamites, and which appears to have been homosporous. We also know that at a 
later stage the true Calamites sprang from rhizomes, with normal nodes and inter- 
nodes, which were very slender, as compared with the typical stems. We are 
indebted especially to M. Granp’Eury for this information... He figures, among 
many other specimens, one of these rhizomes, which gives off from several points 
stems of the normal Calamitean type. These stems, though merely preserved as 
sandstone medullary casts, devoid of all traces of xylem or cortex, are many times 
larger than the rhizome from which they spring. We unfortunately know nothing of 
the organization of these rhizomes. If their structure should turn out to be simpler 
than that of the normal stem of Calamites, we may find in them an early stage of 
development of the plant. 
We cannot doubt that Calumites, like the Hquiseta, and all recent Vascular Crypto- 
gams, possessed a sexual prothallus, though its discovery is doubtless impossible. 
We may conjecture that the first product of the prothallus after fertilization may have 
* Such as that figured in Wi.tiamson, ‘ Organization,” Part XII., Plate 27, fig. 3. 
+ Loc. cit., Part XIT. 
ft Wituiamsoy, “ Organization,” Part L., Plate 25, fig. 16. 
§ Wintiamson, loc. cit., Part 1X., p. 319. 
|| The name which we propose to give to the strobilus described by WiLLIamson, in “ Organization,” 
Part XIV. See below, p. 916. 
| ‘Flore Carbonifére du Département de la Loire, &c., 1877. 
