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conditions of temperature which enable us to observe the reversal now of this set of lines, now of that, the more complex becomes the possible origin. Some spectra are full of doublets : sodium and potassium, as ordinarily mapped, may be said indeed to consist exclusively of doublets; others, again, are full of triplets, the wider member being sometimes on the more, sometimes on the less, refrangible side. Doublets and triplets, as a rule, reverse themselves more freely than the irregular lines in the same spectrum-which particular doublet or triplet will reverse depending upon the temperature, as if the cooler vapour to which the .reversal is due varied as in the case of fractional distillation. Some lines are clean cut in their reversal ; others, again, to use the laboratory phrase, are fluffy to a degree that must be seen to be appreciated, so much so, that when photographed they appear merely as blurs upon the plate.

The above results, which have been foreshadowed in my previous papers, have led me to examine especially the intensities of the various Fraunhofer lines, and to compare the intensities of the metallic lines confronted with them in arc and sun photographs. I have done this because it is worse than useless to proceed with this construction of the large map now that four years' work has shown that the method of impurity elimination has proved insufficient, until some other method, embodying a higher law, can be used ; and to get this we want work over the whole field. This examination I am making, not only from K to G, over which my own photographs extend, but even to b, by means of another series taken by Professor Roscoe, which he has allowed me to inspect.

In short, in this survey I have about 300 photographs to work upon. I exhibit several of these photographs to the Society in anticipation of a further communication.

The upshot of this inquiry even already is as follows:-The discrepancy which I pointed out, six years ago, between the solar and terrestrial spectra of calcium is not an exceptional, but truly a typical

Variations of the same kind stare as in the face when the minute anatomy of the spectrum of almost every one of the so-called elements is studied. If, therefore, the argument for the existence of our terrestrial elements in extra-terrestrial bodies, including the sun, is to depend upon the perfect matching of the wave-lengths and intensities of the metallic and Fraunhofer lines, then we are driven to the conclusion that THE ELEMENTS WITH WHICH WE ARE ACQUAINTED HERE DO NOT EXIST IN THE SUN.

case.

March 27, 1879.

THE PRESIDENT in the Chair.

The Presents received were laid on the table, and thanks ordered for them.

The following Papers were read :

I. “On the Organization of the Fossil Plants of the Coal

Measures. Part X.” By W.C. WILLIAMSON, F.R.S., Professor of Natural History in Owens College, Manchester. Received March 5, 1879.

(Abstract.) The still existing differences of opinion respecting the botanical affinities of the Sigillariæ give value to every new fact calculated to throw light upon the question. In 1865, Edward Wunsch, Esq., of Glasgow, made a discovery, which proves to have an important bearing upon it. He found, at Laggan Bay, in Arran, a series of rather thin Carboniferous strata, separated by thick beds of volcanic ash, and in one of the Carboniferous shales especially, he discovered the bases of the stems of numerous very large trees, standing perpendicularly to the shales. These trees have been referred to by several authors as Sigillarian. In the summer of 1877, Mr. Wunsch and I employed quarrymen to make extensive excavations amongst these strata, for the purpose of adding to the extensive series of specimens which he had obtained, and the whole of which he kindly placed in my hands. The aggregate result of these explorations was to show that the conclusion previously arrived at, viz., that the stems had belonged to a grove of Sigillarian trees was unsupported by a solitary fact. These stems were of very large size, showing that they had belonged to fully grown trees. None of them displayed any traces of leaf-scars, having outgrown the stages at which such scars would remain visible. Their outer surfaces were scored with deep irregular longitudinal fissures, resulting from internal growth and consequent expansion, and which appear to have been mistaken for the longitudinal grooves and ridges of a Sigillarian bark. Such, however, they certainly were not, since, in every instance, the surface bark had been entirely thrown off, and the fissures entered deeply into the subjacent bark layer. In most of the stems, this comparatively thin bark layer was the only one that remained, the greater portion of the inner bark and the central vascular axis having disappeared, leaving a large cylindrical cavity, which was

filled

up

with volcanic ash. These stems failed to display a single feature, justifying the conclusion that they were Sigillarian.

In two of them the central cavity, instead of being filled with ash, was filled with miscellaneous heaps of vegetable matter, amongst which were large fragments of the vascular axes of various plants, such as Lepidodendra and Stigmariæ, but in one of the largest stems were five or six decorticated vascular cylinders of Diploxyloid stems, of the largest size, and which, though arranged parallel to the long axis of the cylinder which enclosed them, obviously did not belong to them, but had been floated in from without. The supposition that these had been young stems that had grown within the hollow protecting cylinders, from spores, accidentally introduced, is wholly untenable, since each one of these several vascular axes has been the centre of a stem fully as large as that within which we found them aggregated. Of course, these Diploxyloid vascular axes had the organization which Brongniart and the younger school of French botanists which still upholds his views on this point, believe to be characteristic of true Sigillariæ-a conclusion from which I have long dissented.

The only fragment we found, that threw any light upon the character of the leaf-scars that had indented the surfaces of these fully grown stems, was a well-defined example of the Lepidodendroid type.

We directed careful attention to the nature of the smaller fragments of branches and foliage which abounded in the volcanic ash with which the large stems were overlaid. These consisted of Lepidodendroid branches and twigs of all sizes and ages, and no doubt was left upon my mind that they were really the disjecta membra of the stems around which they were so profusely scattered. The only fruits that have been obtained from the same locality are Lepidostrobi, most of which contain macrospores and microspores. Unless we are prepared to believe that this Arran deposit contained, on the one hand, numerous stems without branches, and, on the other, yet more numerous branches without stems, we must recognise in these specimens the complementary elements of a grove of Lepidodendroid trees. One specimen found is a very important one.

It has a mean diameter of six inches, and is either a small stem or a very large branch. Internally it exhibits the same structure as all the smaller Lepidodendroid branches, except so far as it is modified by size and age. But in addition to its other features, it exhibits a very narrow exogenous ring surrounding the ordinary Lepidodendroid one, thus giving some clue to the size attained by such branches before the internal organization passed from the Lepidodendroid to the Sigillarian type.

I have at last succeeded in obtaining the Strobilus, to which the remarkable macrospores and microspores figured in my last memoir belong. It unexpectedly proves to be a very small one, being little more than an inch in length. Further specimens have shown that the abnormal peduncles of the macrospores shown in Plate 23, fig. 64, are wholly due to the partial collapse of the spore-wall. Further specimens have also been obtained of the Strobilus and its spores represented in Plate 22, figs. 38–57. These examples possess the central vascular axis in a perfect state, which portion was lacking in the previously known examples. It proves to have an individuality as distinctive as that of the spores and sporangia which it bore.

The important discovery by Mr. D'Arcy Thompson, of Edinburgh, of young branches of Ulodendron with reproductive cones actually attached to the scars characteristic of the genus, finally settles the nature and functions of these scars, showing that they mark the positions from which bilaterally arranged deciduous organs of fructification have fallen.

The structure of Calamostachys Binneyana has had further light thrown upon it, sustaining my previously expressed convictions that it had a triquetrous axis, and that consequently its affinities were with Asterophyllites and Sphenophyllum, and not with Calamites. A specimen demonstrates that the six vascular bundles going to the six fertile sporangiophores were given off in pairs from the three truncated angles of a triangular vascular axis—an orientation absolutely identical with that represented in similar sections of stems of Sphenophyllum, published by M. Renault. The recent discovery by Herr Stur, of Vienna, of a plant in which Sphenophylloid and Asterophyllitean leaves are found upon a common stem, establishes the correctness of my previous conclusions as to the very close affinities of these two genera.

Two new fern petioles or stems have been obtained from Halifax, to which I have given the name of Rachiopteris robusta and R. insignis. In one specimen of the latter, the large vessels of the central bundle are full of Tylose cells, whilst a second example exhibits no trace of them. This shows the existence or non-existence of Tylose to be a characteristic having no specific value.

Since my last memoir was written I have obtained several new forms of cryptogamic conceptacles-similar to those previously described under the generic name of Sporocarponas well as been able to throw additional light upon some of those previously described. No clne has yet been obtained as to the plants to which these very remarkable organisms belonged.

A large series of specimens from Oldham and Halifax has enabled me to investigate in detail the very curious objects to which Mr. Carruthers gave the name of Traquairia, and which that observer believes to be a form of Radiolarian life. Their

very elaborate organization can scarcely be made intelligible without the aid of plates. In a

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