effect is attributed in the north, in causing the disappearance of rare plants, has none at Montpellier, for there are no bogs to drain; and the vast lagoons and marshes which border the Mediterranean still occupy at least as great an extent as they did some centuries back. When waste lands are broken up they are rarely enclosed, and from the broken, rocky nature of the country, scattered spaces are usually left undisturbed, quite sufficient to perpetuate the previous wild vegetation. If the conversion of the forest of Gramont, below the town, or of the greater part of the rocky hill of Cette, with vineyards and olive-grounds, the disappearance of the few meadows of Boutonnet, or the reduction of the once extensive woods of Pinus halepensis, around Montferrier, may have spoiled some of the best herborising grounds of the botanists of the sixteenth or seventeenth centuries; on the other hand, a few miles further north, from Montferrier to beyond the Pic St. Loup, many a ruin of cottage or castle, barn or enclosure, many an ancient track of the spade or plough in what is now the open garrigue, or wild barren pasture of the country, show the extent of land, or at least the numerous patches, once under cultivation, but now again left to the operations of Nature, checked only by the ravages of the real enemies of scarce plants -the flocks of sheep and goats that roam over them, and the countless swarms of the insect tribe.

Cultivation alone has, therefore, had but very little effect in destroying established species, and still less the wanton efforts of botanical collectors. Montpellier has indeed had her dealers or even amateurs who, after having supplied themselves with what they conceived a sufficient stock of specimens of some of the rarer species, have used every exertion to destroy the remainder; but they have not succeeded. Lavatera maritima, Pastinaca Opopanax, Diplotaxis humilis, etc., are still to be met with. Even the exertions of gardeners to collect for planting all the roots they could find of Pancratium maritimum, and some other Liliacea and Orchideæ, from their very limited stations, have not yet effected their extirpation.

Dr. Planchon finally alludes to another cause of destruction, in a manner which shows how steadily, although gradually, thinking naturalists on the Continent, in spite of opposition, are adopting one of the important principles laid down by Lyell and Darwin, that of gradual change through countless ages versus sudden catastrophes. "This cause," he says, "is the action slow but sure of the thousand often inappreciable modifications, by which nature gradually substitutes new species for the preexisting ones. This succession of vegetable

forms, in one and the same region, is a well-established law, and without going back to geological periods, when it presents itself to us on an immense scale, we can recognise its effects in the present period." After alluding to the substitution of one tree for another as the prevailing essence of forests, as observed in other countries, and to the disappearance of trees and shrubs common in former ages about Montpellier, as more especially considered in the memoir we shall revert to further on, he further observes:

"But if the operations of Nature are carried on with a certainty that our feeble means never obtain, it is also with the slowness of a power that has ages at its disposal. Nothing, therefore, is more difficult to establish than this gradual progress of certain species towards destruction during periods when the action of physical causes can be leisurely exercised without being disturbed by human intervention.

"To such a cause may, perhaps, be attributed the local disappearance of trees formerly common in some of our woods: the Nut tree and the Holly, much less frequent in the low grounds than they used to be; the Sycamore indicated by Magnol and Gouan at the Capouladoux, but which, to our knowledge, has not been found there in our days. These are, however, probabilities only; man may have assisted nature and hastened the loss of these species in restricted localities. At all events it will require much time yet before the work of their destruction is completed over our whole region; and before these species, scattered here and there in the Cevennes, can be entered in the list of our extinct species." We may suggest in addition, that these three trees, as well as the wild. gooseberry, alluded to by Planchon as disappearing also from the low ground, all thrive best in a more temperate climate, and that the additional exposure, occasioned by the destruction of woods, may have been the last stroke that disabled them from resisting the difficulties they had to contend with during the burning Montpellier

summer.

As the general result of physical causes, combined with human action, Dr. Planchon can only establish the loss from the region of Montpellier of five species since the sixteenth century. Five species, however, in three centuries, might be considered as a large number in proportion to what has been observed elsewhere, if all five had been really old well-established species. But two of them, Lupinus luteus and L. varius, from the details he gives further on; can scarcely have been more than weeds of cultivation, and should

probably have been classed with the more or less temporary intruders, spoken of under the head of introduced plants. The three others, Clematis recta, Coronilla juncea, and Arum arisarum, are still not uncommon in some parts of Provence to the east, and in Catalonia to the south-west, and are most probably species which in fact are slowly but steadily losing ground.

In investigating the causes of introduction and dispersion of new species, Dr. Planchon has been unable to trace any results within the last three centuries to the action of purely physical causes, such as currents of water or wind, or to the action of animals independently of man. The Montpellier seaboard is not exposed to any extensive maritime currents, which, on some of our own and other Atlantic coasts, bring seeds from great distances rapidly enough to preserve their powers of germination, and if, as is most likely, some are brought from smaller distances, and germinate and grow, they are the same which have done so repeatedly during tens or hundreds of centuries, and cannot be distinguished from those raised from native seeds. Fresh water currents can still less have introduced foreign plants, for every stream of the region rises within it. All that they can do is occasionally to bring down mountain plants into the valleys, or to disperse along their banks species otherwise introduced. The action of winds and that of animals, always independently of human agency, take effect chiefly within limited distances; and in this respect the same observation applies to them as to that of the sea, that the present conformation and condition of the country has lasted so long, that their force has long since had its full effect, and they have no new plants to act upon, unless brought within their influence by other means. The only new species which the author thinks may possibly have been introduced by these means, is the Erigeron canadense, which the winds may have brought into the region from other parts of France, where it had previously established itself. It must, however, be recollected, that whatever be the means by which a plant is first introduced into a region, it is, according to the definition of the term, by the action of physical causes alone that it can be naturalized—that is, maintained, propagated, and dispersed without human protection or aid.

All means of introduction, independently of the above-mentioned regular physical causes, are, unless some great change takes place in the physical conformation, climate, or other condition of the country, reduced to the direct or indirect influence of human agency.

The most important and direct influence of man is by cultivation. "Wherever he has established himself, he has deeply modified the aspect of vegetation; he has broken up large tracts, covered them with plants foreign to the country, and, by his constant care, protected against the attacks of the indigenous vegetation, those plants necessary for his wants or his industry. But this introduction of cultivated plants does not enter within the scope of our essay; we only take into consideration those species which, once confided to the soil, are abandoned to their own resources, and must maintain themselves, without other aid, against the enemies of all kinds which surround them."

But direct efforts have not been wanting on the part of botanists really to naturalize exotic plants in various parts of the region by sowing and planting them in localities where they were supposed to be likely to succeed. Nissole in the seventeenth century, Gouan and Amoreux in the eighteenth, and Moquin-Tandon in the present one, carried on the operation on a large scale. Gouan and Amoreux especially have left records of about 900 species so treated; but after a careful research, Dr. Planchon cannot discover that a single one has established itself, or is now to be found in the localities indicated, if it was not already naturally there. It is true that, on examining the lists, there appears to have been very little discernment on the part of the experimenters in the selection of species or of stations. "They have taken into account neither the favourite stations of these species, nor the aspects which they usually prefer, nor the chemical or physical condition of the soil, nor the association of the vegetation which surrounds or shades them." It is probable also that the number of seeds sown, or of roots planted, was always very limited. "It is, therefore, not surprising that the rare individuals which succeeded in germinating, isolated amidst the rightful possessors of the soil, should rapidly have been smothered by them." But it is observed, "notwithstanding the imperfection of these attempts, it must be admitted that some species amongst the number must have met with the conditions favourable for their development. Why have they not spread and established themselves in the country? It is evidently because the naturalization of a plant meets with many more difficulties than one would suppose without experience. There are indeed very few that triumph over all the obstacles opposed to their establishment. If a species does not early show its tendency to naturalization, if it does not sow or multiply itself on its arrival

in the country, one must inevitably expect a failure in endeavouring to introduce it."

In recent days, a few attempts, made with more judgment and perseverance, have met with rather better success, but only in the case of aquatic plants propagated by their rhizomes. Three of these appear to be more or less established: Aponogeton distachyon in the Lez at Lavalette, planted in 1838; Acorus calamus in the pool of Gramont, planted in 1849; and Jussieua grandiflora, thrown into the Lez many years since, and now spread all along its course from Pont Juvenal downwards.

The indirect or involuntary agency of man has been here, or elsewhere, much more effective in the introduction and naturalization of new species. This takes place by the natural propagation and dispersion-1, of plants cultivated in fields or gardens; 2, of weeds or other plants whose seeds have been sown with imported grain or cast aside in picking it; 3, of seeds imported with wool, ballast, or other substances spread out or heaped up on waste places.

The escapes from cultivation permanently established in the neighbourhood of Montpellier during the three centuries, have been remarkably few. Of the numerous species cultivated in the botanic garden since its establishment in the eighteenth century, although several have spread as weeds within the enclosure, and five have even extended beyond, two only - Hypecoum procumbens and Veronica peregrina-have become really naturalized in the neighbourhood, and those to no great distance. Besides these, the only cases within the region which Dr. Planchon has been able to ascertain, are those of Cyclamen hederafolium, established for the last century at Chateaubon, near Montpellier, but which has not passed the limits of the park; and of Enothera biennis, now scattered here and there along streams and in sandy places, but whether escaped from local gardens, or gradually spread from other parts of France, where it had been similarly introduced, is uncertain.

The weeds of cultivation of ancient introduction are undoubtedly numerous; but the additions within the last three centuries are limited to six species, viz., Amarantus albus and A. retroflexus, Xanthium spinosum and X. macrocarpum, Erigeron canadense, and Bidens bipinnata, all (except, perhaps, Xanthium macrocarpum) of American origin, and all now abundant in vineyards and other cultivated and waste places. Of these, the Erigeron, the Bidens, and the Xanthium spinosum, appear to have been first noticed in the last century, the