242 



HARDWICKE'S SCIENCE-GOSSIP. 



the bark, which in this root is almost always pre- 

 served ; but for reasons which I will briefly indicate, 

 I have not thought it advisable to give this root a 

 name at present. I have already pointed out that 

 under the name of Astromyelon a very widely diver- 

 gent series of plants are comprehended, which may 

 probably have to be divided into two or more species 

 when we have learnt more about them. The common 

 form, with the star-like pith, will form one group ; 

 while those with little or no pith, may form another 

 group. In that case, the new root which I have 

 named Amyelon radiatus would most probably belong 

 to the former, while the other would agree with the 

 latter group. I am not however, quite satisfied about 

 placing the pithless stems of Astromyelon along with 

 the true "star-like" pithed ones, and it is only 

 because of my inability to draw a dividing line 

 between the two groups that I have done so. It is 

 quite possible that these pithless stems may have 

 been underground stems or rhizomes, and in that case 

 my second roots might simply be their smaller 

 branches. 



But whether stems or roots, they are quite laew, 

 and I trust of sufficient interest to be brought before 

 you, if only to show you what a wide field there is 

 still open for further researches in this most interest- 

 ing subject. 



I have already pointed out to you that the woody 

 cylinder of Astromyelon bears a general resemblance 

 to that of Calamites. I wish now to draw your 

 attention to the structure of Asterophyllites. The 

 beautiful forms of this plant have long been known 

 to collectors of fossil plants. It derives its name 

 from the fact of its long narrow leaves being arranged 

 in whorls at intervals along the stem, in a star-like 

 manner. The highly specialised character of the 

 tissues of this plant was unknown until a few years 

 ago. It was for some time regarded even as the 

 young branches and leaves of Calamites, along with 

 Sphenophyllum and Annularia. But the discovery 

 of its stems in our coal-balls has shown that it is an 

 independent genus. 



In the French coal-fields Sphenophyllum has also 

 been found, with the structure preserved, and its 

 structure is found to closely resemble that of our 

 Asterophyllites. But up to the present date neither 

 Sphenophyllum nor Annularia have been recognised 

 in our coal-balls. A single glance at the structure of 

 the transverse sections of Calamites and Asterophyl- 

 lites will be sufficient to show how widely they differ 

 from one another. In Calamites the woody cylinder 

 is composed of an indefinite number of wedges, 

 varying from eleven to sixty or more, according to 

 the size of the plant. But in Asterophyllites there 

 are only three large ones, and this number never 

 varies, being the same in young and old alike. But 

 there is a much greater difference between the two 

 plants in the form of the pith, which, as I have 

 already pointed out, is fistular in Calamites, whereas, 



on the other hand, the centre of the stem of Astero- 

 phyllites is seen to be occupied by a remarkably 

 characteristic pith, which is triangular in form and is 

 composed of vascular tissues, like the pith of Lepido- 

 dendroid plants. From each of these angles is given 

 off a woody wedge, which are very small in young 

 plants, and the spaces between them are filled with 

 parenchymatous tissues ; but in older stems these 

 wedges increase in size, until they form a solid 

 cylinder. The general character of these wedges is 

 the same as those in Calamites and Astromyelon. 

 But the structure of the bark is different from that of 

 either of the latter plants. The cells are square or 

 oblong in form, and have thicker walls, which accounts 

 for their being generally more or less preserved. Then 

 again, the stems of Calamites are strengthened 

 internally by the intercrossing of the wedges at the 

 nodes ; whereas the solid pith of Asterophyllites is 

 continuous throughout the stem, and there is an ex- 

 ternal swelling at each node where the leaves and 

 branches were given off. We need scarcely add that 

 stems possessing such differences in structure as these 

 do could not possibly belong to one and the same 

 plant. Moreover, Calamites with branches are not 

 unfrequently met with, and the structure of these 

 branches is identical with that of their parent 

 stems. 



From the foregoing brief account of Astromyelon 

 and its allies, it will be seen that while there are 

 many points in which they differ widely from one 

 another, yet in regard to the most important part of 

 their structures they are bound together by the most 

 intimate ties of relationship. The woody wedges of 

 the ligneous zone in each of the three genera are 

 constructed on the same plan, and formed of the 

 same kind of tissues. In each genus the wedges or 

 bundles are open, and as the plants increased in size 

 they also increased in size by the addition of new 

 cells and vessels in a truly exogenous manner. 



It is also important to bear in mind the fact, that 

 although the great majority of our coal-ball speci- 

 mens in each genus belong to small herbaceous 

 plants, yet there is abundant evidence to prove that 

 a large number of plants attained to arborescent 

 dimensions. These facts have an important bearing 

 upon the great question of evolution. 



Though forming part of the great group of Crypto- 

 gams, yet they have had many affinities with the 

 fossil pines of the same age. The mode of growth 

 and construction of the ligneous cylinder is homolo- 

 gous with what obtains in Dadoxylon and in Lygino- 

 dendron, while their scalariform and parenchymatous 

 tissue are homologous with similar tissues in the 

 Lepidodendroid plants. 



Our interest in these pretty plants is not yet 

 exhausted, for only so recently as the last few months 

 some interesting discoveries have been made in con- 

 nection with them. Hitherto the bark of Astro- 

 myelon has neither been described nor figured ; it 



