XX.-DIE FARBEN DER PFLANZEN. Von G. von Martens. Württ. Jahreshefte, 1862, p. 239.

THE first short chapter of this essay on Colour in the Vegetable Kingdom is upon the Rainbow, and is headed with a verse from Sirach (ch. xliii. 12). The second is upon the Prism and Spectrum. We pass these by and confine ourselves to a brief resumé of some of the author's painstaking inquiries into the colour-relations of the several organs of plants, of the flowers of widely different Floras, and of different Natural Orders. We devote the space to this the more willingly, that we believe such inquiries carefully carried out, and resting upon a basis sufficiently broad, often afford unexpectedly interesting results. In connection with the special inquiry pursued by Hr. von Martens, such results can hardly be said to have been as yet forthcoming, though this may be attributable to its neglect by competent botanists rather than to any cause more deeply seated. Since the observations of Professor Dickie, recorded in the Annals of Natural History* some eight years ago, we do not recollect any contribution of scientific importance upon the colour-relations of plants in our own or foreign journals. Prof. Dickie's paper was especially upon the complementary relations of colours in the individual and the relation between the form and colour of organs,branches of the subject which do not appear to have specially engaged the attention of our author.

In the third chapter we have a description of the Chromatic Table, similar to that in Chevreul's well-known work, which accompanies the essay. It is a circular disc divided by twenty-four equi-distant radii into as many wedges, each coloured in one hue and decreasing in intensity from the centre to the margin in eight degrees of tone-(Farbentonleiter-Gamme, Chevreul). Some such chromatic table is essential in inquiries of this kind, and until a better be decided upon, we are content to pin up Hr. Marten's disc in our plant room, and to respect his nomenclature with but few exceptions, which do not detain us now. In the eleven succeeding chapters, the several organs of the plant are seriatim examined with respect to their colour-phenomena. We have not, generally, the successive changes traced through which the plant or an individual organ passes from youth to age, but commencing with the lowest member of the structure, the root, and continued through stem, leaf, flower, fruit and seed, we have recorded several observations of considerable interest, among the more important of which are those upon the colour-relations of the flowers of different Floras. In Hr. v. Martens' method of collating these we find some awkward peculiarities which the friendly

* Ser. ii. xiv. 401.

revision of some practical mind might perhaps have spared him. Thus he gives us the total number of flowering plants of a given area, then deducts the apetalous and glumaceous species, and those destitute of petaloid perianth; then, whatever be the number of these species bearing flowers of two colours, we have such number added to the above. The proportion of this new total with white flowers is next stated, and then follow the percentages of the respective colours based upon their own total, remaining after the white-flowered species are deducted. It may be all very well to put the matter in this way, but certainly not only thus.

The relative prevalence of the several colours is inquired into under the heads of (1) the wild and cultivated species of Württemburg, (2) the Flora of the Alps, (3) of Greenland, (4) of Spitzbergen, (5) of the littoral Flora of Europe; and, further, in respect to the season of the year; the various natural orders; and, finally, the odour of the flower. It is to be regretted that our author should have been willing to accept to so great an extent as authority for the colour of the flowers of the various Floras treated of, the plates of Flora Danica' and the works of Jacquin and Sturm. As to the species of Greenland, he acknowledges himself wholly indebted to the plates of Flora Danica,' while the colours of Spitzbergen flowers were adopted, in turn, from their Greenland and Alpine representatives. With such guides it must have been impossible to avoid much error, especially in the attempt to classify the flowers according to their depth of tone.

The Flora of the Alps includes 481 species, of which 93 are reckoned as apetalous or glumaceous. Deducting these, Hr. v. Martens adds 61 to the remaining 388, 61 being the number of species bearing two-coloured flowers. 115 of the 449, or a little above one-fourth, are white-flowered. These are deducted, leaving 334 with coloured perianths. Yellow obtains more or less in 35 per cent. of these, blue in 40 per cent., and red in 47 per cent. This apparently small proportion of the yellow series is explained by the independence of this colour in Alpine flowers. While 13 species have flowers of pure blue and but two pure red, 108 are pure yellow. On the other hand, of yellow in combination, but 44 tend towards red and 4 to blue, while 163 exhibit various combinations of red and blue. In the Greenland Flora 329 species are reckoned,* of which 137 are destitute of petaloid perianths. 69, or more than one-third, of the remaining 192, are white-flowered. 51 are pure yellow, 11 yellow mixed with red, and 5 yellow with blue. There are no pure red flowers, and but 2 pure blue, though there are 58 of shades intermediate between blue and red. But 74 Phanerogams are known to the author from Spitzbergen. As in Greenland, yellow greatly predominates, both in purity and frequency.

* Reduced in Dr. Hooker's "Arctic Flora" to 281 species.

In regard to the littoral Flora, which Hr. Marten believes to present a greater contrast than any other in Europe with the Floras of the Alps and Arctic Circle, comparisons rest on the species growing on the shores of Denmark, Germany, and Italy. This peculiar Flora includes 217 Phanerogams, 87 of which are apetalous or glumaceous, and 25 are white-flowered, leaving a balance of 105 with coloured perianths. Of these, 4 species are two-coloured, 21 are pure yellow, 17 yellow and red, 3 yellow and blue, with 1 pure red and 1 pure blue, against 59 intermediate between red and blue. Compared with Greenland, it is shown that, in the littoral Flora, the proportion of species, destitute of coloured perianth, is about the same: the chenopods of the sands balancing the sedges of the snow. That the white flowers are only about half as numerous, the yellow fewer, the red rather more, and the blue nearly twice as numerous. In the species of the Württemberg Flora, the largest proportion with white flowers expand in spring, and suggest the notion that the lower the temperature, the more numerous they become. Red flowers predominate in autumn and summer; yellow constitute an equal proportion in spring, summer, and autumn; while blue, like white, decreases from the first.

Of the species with agreeably scented flowers growing about Württemburg, the largest proportion are white-flowered, the second red. Pollen is almost always yellow, or some colour in which it forms part. The few observed exceptions are recorded. Finally, the principal groups of Cryptogams are severally noticed in respect to their colour-relations.

234

Original Articles.

XX.-HEINRICH RATHKE.-ON THE DEVELOPMENT OF THE CRANIUM IN THE VERTEBRATA.

[The active and long continued labours of the head and founder, after Van Baer, of that modern science of Embryology which is the necessary precursor of all philosophical anatomy worthy of the name, are now unfortunately ended, Professor Rathke having died suddenly and unexpectedly while presiding over the Scientific Congress which met in Konigsberg three years ago. So long as the venerated master lived, it behoved those who had learned so much from him respecting the development of the vertebrate skull to wait for the fulfilment of the promise half given in the opening paragraphs of the masterly essay here translated. But there is no sign that any larger work on this subject remains among the papers of the deceased philosopher, and therefore, the translator, imagining that others may find it as difficult as he has done to procure the original "Vierter Bericht über das naturwissenschaftliche Seminär bei der Universität zu Königsberg-nebst einer Abhandlung über die Entwickelung des Schädels der Wirbelthiere," published at Konigsberg thirty-four years ago, (1839) offers this version of a memoir which is at this moment the best and most comprehensive account of the development of the skull extant. Hereafter the translator will take occasion to point out how far later inquiries by Rathke, or by others, may necessitate the modification of some of the paragraphs of this essay.—T. H. H.]

§1. WHILE occupied during the last few years, with investigations into the development of the Snake, I was much surprised at the mode in which the formation of the skull commenced-and I was thus induced to examine the same process in other vertebrata ; the more especially as I entertained the hope that the study of its development would tend to elucidate the view that the skull is composed of several modified vertebræ.

But in putting forth the results of the observations bearing on this question, which I have made, it must be remembered that they are but the outlines of a work, which I propose to complete by further researches.

§ 2. If any trustworthy result is to be attained from attempts to explain the skull as consisting of several modified vertebræ, they must be based on an acquaintance with the development of the spinal column. Therefore I shall premise an account of the most essential steps in the development of that part.

§ 3. That which constitutes the foundation of the spinal column, is the notochord, a membranous tube, closed on all sides and filled with a gelatinous substance. Hence the notochord consists, in and for itself, of two different parts which may be termed the axial substance and the sheath. Round it is deposited a blastema, which at first, has the same coarsely granular composition throughout. It seems to make its appearance first on the right and left sides of the notochord, and then gradually to grow above and below round the notochord, so that after a certain time, the latter is coated with it, as by a new or second

sheath. However this may be, the substance of this blastema, which I term the Investing mass of the notochord, very soon increases, chiefly in thickness, on each side; the thickening not being alike in all parts, but in some places thicker and in others thinner. This takes place in such a manner, that, on each side, a multitude of small plates are formed, of which each pair have a small, thinner, interspace. By degrees the plates grow towards one another above and below, and at last each pair coalesce into a ring. Consequently after a certain time the notochord is seen to be inclosed within a number of such rings, which lie in a series one between the other.*

But before the plates thus coalesce into rings, the investing mass of the notochord, whence they are developed, grows upwards on the two sides of the future spinal cord, within the dorsal laminæ, and here also attains, in one spot a greater, in another a less, thickness. These thicker and thinner spots correspond with the similar parts of the investing mass on the two sides of the notochord, or rather are to be regarded as the prolongations of them.

Thus, after a certain time, there arises an appearance as if the just mentioned and already completed rings which inclose the notochord, had sent up rays to embrace the spinal cord on both sides. Later still, each pair of these rays come into contact above the spinal cord and coalesce, so as to form arches, which are borne by the rings inclosing the notochord. In the tails of osseous fishes, the same process goes on towards the opposite side, but the arches thus formed inclose, not parts of the nervous system, but the caudal arteries and veins. In the trunk of osseous fishes also, the rings which indicate the bodies of the vertebræ throw out downwardly directed processes and, in certain fishes, the hindermost of these also coalesce so as to form arches; ordinarily, however, they remain separate from one another, but mark themselves off from the bodies of the vertebræ and then appear as ribs. As in Fishes, so in other Vertebrata, processes are developed from the investing mass of the notochord in the trunk, and serve to inclose the subjacent viscera more or less completely. Some of them become distinct, either close to the rings, from which the bodies of the vertebræ will be formed, or at some distance from them, and are either developed into ribs only, or into ribs and transverse processes; others do not become distinct, and acquire the character of simple transverse processes. The transverse processes which are formed in many caudal vertebræ of different Amphibia and Birds have a similar origin.

It is to be remarked that in some Amphibia, below these transverse processes, additional paired processes are formed, which in the Crocodiles coalesce into arches, but in the Snakes remain

Whether in many or in most Vertebrata two series of such plates, an upper and a lower (which however soon coalesce), are developed on each side, as is said by Von Baer to be the case in Cyprinus blicca requires further investigation. It is certainly not the case in the Snake.