by M. de Senarmont by means of artificial crystallizations. (Ann. de Chim. 3 Ser. xli. p. 319.)

M. Pasteur has found that Racemic Acid consists of two different acids, having the same density and composition. The salts of these acids, with bases of Ammonia and of Potassa, are hemihedral, the hemihedral faces which occur in the one being wanting in the other. The acids of these different crystals have circular polarization of opposite kinds. (Ann. de Chim. 3 Ser. xxviii. 56, 99.) This discovery was marked by the assignation of the Rumford Medal to M. Pasteur in 1856.

M. Marbach has discovered that crystals of chlorate of soda, which apparently belongs to the cubic or tessular system, exhibit hemihedral faces of a peculiar character; and that the crystals have circular polarization of opposite kinds in accordance with the differences of the plagihedral faces. (Poggendorf's Annalen, xci. 482.)

M. Seydolt of Vienna has found a means of detecting plagihedral faces in quartz crystals which do not reveal them externally. (Akad. d. Wissenschaft zu Wien, B. xv. s. 59.)

3. Classification of Minerals.

In the Philosophy of the Inductive Sciences, B. VIII. C. iii., I have treated of the Application of the Naturalhistory Method of Classification to Mineralogy, and have spoken of the Systems of this kind which have been proposed. I have there especially discussed the system proposed in the treatise of M. Necker, Le Règne Mineral ramené aux Méthodes d'Histoire Naturelle (Paris, 1835). More recently have been published M. Beudant's Cours élémentaire d'Histoire Naturelle Minéralogie (Paris, 1841); and M. A. Dufresnoy's Traité de Minéralogie (Paris, 1845). Both these works are so far governed by mere chemical views that they lapse into the inconveniences and defects which are avoided in the best systems of German mineralogists. The last mineral system of Berzelius has been de

veloped by M. Rammelsberg (Nürnberg, 1847). It is in principle such as we have described it in the history. M. Nordenskiold's system (3rd Ed. 1849,) has been criticised by G. Rose, who observes that it removes the defects of the system of Berzelius only in part. He himself proposes what he calls a 'Krystallo-Chemisches System,' in which the crystalline form determines the genus and the chemical composition the species. His classes are

1. Simple Substances.

2. Combinations of Sulphur, Selenium, Titanium, Arsenic, Antimony.

3. Chlorides, Fluorides, Bromides, Iodides.

4. Combinations with Oxygen.

We have already said that for us, all chemical compounds are minerals, in so far that they are included in our classifications. The propriety of this mode of dealing with the subject is confirmed by our finding that there is really no tenable distinction between native minerals and the products of the laboratory. A great number of eminent chemists have been employed in producing, by artificial means, crystals which had before been known only as native products.

BOOK XVI.

CLASSIFICATORY SCIENCES.

FOR

BOTANY.

OR the purpose of giving to my reader some indication of the present tendency of Botanical Science, I conceive that I cannot do better than direct his attention to the reflexions, procedure, and reasonings which have been suggested by the most recent extensions of man's knowledge of the vegetable world. And as a specimen of these, I may take the labours of Dr. Joseph Hooker, on the Flora of the Antarctic Regions,1 and especially of New Zealand. Dr. Hooker was the Botanist to an expedition, commanded by Sir James Ross, sent out mainly for the purpose of investigating the phenomena of Terrestrial Magnetism near the South Pole; but directed also to the improvement of Natural History. The extension of botanical descriptions and classifications to a large mass of new objects necessarily suggests wider views of the value of classes (genera, species, &c.), and the conclusions to be drawn from their constancy or inconstancy. A few of Dr. Hooker's remarks may show the nature of the views taken under such circumstances.

I may notice, in the first place, (since this work is intended for general rather than for scientific readers,) Dr. Hooker's testimony to the value of a technical descriptive language for a classificatory science-a Terminology, as it is called. He says, 'It is impossible to write Botanical descriptions which a person ignorant of Botany can understand, although it is supposed by

The Botany of the Antarctic Voyage of H. M. Discovery Ships Erebus and Terror, in the years 1839-1840. Published 1847. Flora Nova Zelandia. 1853.

many unacquainted with science, that this can and should be done.' And hence, he says, the state of botanical science demands Latin descriptions of the plants; and this is a lesson which he especially urges upon the Colonists who study the indigenous plants.

Dr. Hooker's remarks on the limits of species, their dispersion and variation, are striking and instructive. He is of opinion that species vary more, and are more widely diffused, than is usually supposed. Hence he conceives that the number of species has been needlessly and erroneously multiplied, by distinguishing the specimens which occur in different places, and vary in unessential features. He says that though, according to the lowest estimate of compilers, 100,000 is the commonly received number of known plants, he thinks that half that number is much nearer the truth. 'This,' he says, 'may be well conceived, when it is notorious that nineteen species have been made of the Common Potato, and many more of Solanum nigrum alone. Pteris aquilina has given rise to numerous book species; Vernonia cinerea of India to fifteen at least. . . . Many more plants are common to most countries than is supposed; I have found 60 New Zealand flowering plants and 9 Ferns to be European ones, besides inhabiting numerous intermediate countries. . . . So long ago as 1814, Mr. Brown drew attention to the importance of such considerations, and gave a list of 150 European plants common to Australia.'

As an example of the extent to which unessential differences may go, he says (p. xvii.), 'The few remaining native Cedars of Lebanon may be abnormal states of the tree which was once spread over the whole of the Lebanon; for there are now growing in England varieties of it which have no existence in a wild state. Some of them closely resemble the Cedars of Atlas and of the Himalayas (Deodar); and the absence of any valid botanical differences tends to prove that all, though generally supposed to be different species, are one.'

Still the great majority of the species of plants in those Southern regions are peculiar. 'There are

upwards of 100 genera, subgenera, or other well-marked groups of plants, entirely or nearly confined to New Zealand, Australia, and extra-tropical South America. They are represented by one or more species in two or more of those countries, and thus effect a botanical relationship or affinity between them all which every botanist appreciates.'

In reference to the History of Botany, I have received corrections and remarks from Dr. Hooker, with which I am allowed to enrich my pages.

P. 220. Note. Nelumbium speciosum, the Lotus of India. The Nelumbium does not float, but raises both leaf and flower several feet above the water: the Nymphaea Lotus has floating leaves. Both enter largely into the symbolism of the Hindoos, and are often confounded.

'P. 225. Note 5. For Arachnis read Arachis. The Arachidna of Theophrastus cannot, however, be the Arachis or ground-nut.

Pp. 257 and 264. For Harlecamp read Hartecamp. 'P. 349. For Karlen read Kalm.

'P. 349. For Asbech read Osbeck.

'P. 253. John Ray. Ray was further the author of the present Natural System in its most comprehensive sense. He first divided plants into Flowerless and Flowering; and the latter into Monocotyledonous and Dicotyledonous :-'Floriferas dividemus in DICOTYLEDONES, quarum semina sata binis foliis, seminalibus dictis, quæ cotyledonorum usum præstant, e terra exeunt, vel in binos saltem lobos dividuntur, quamvis eos supra terram foliorum specie non efferant; et MONOCOTYLEDONES, quæ nec folia bina seminalia efferunt nec lobos binos condunt. Hæc divisio ad arbores etiam extendi potest; siquidem Palmæ et congeneres hoc respectu eodem modo a reliquis arboribus differunt quo Monocotyledones a reliquis herbis.'

'P. 282. Endogenous and Exogenous Growth. The exact course of the wood fibres which traverse the stems of both Monocotyledonous and Dicotyledonous plants has been only lately discovered. In the Monocotyledons, those fibres are collected in bundles, which follow