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difference of opinion. M. Decaisne became first known, when aidenaturaliste at the herbarium of the Paris Museum, by some able monographs, especially that of the Lardizabaleao, which at once gave him a high rank among systematists. In the subsequent elaboration of the Asclepiadea) for De Candollo's Prodromus, he had to deal with characters, difficult from their minuteness and from the care required in extracting them from dried specimens, but which proved to be comparatively constant in species; and thus he was early led to attach much importance generally to those slight differences upon which modern species are established in other orders. But having now, for above twenty years had the general direction of the Jardin dea Plantes, and the superintendence of its cultivation, the opportunities he has had of watching successive generations of plants, and tho elaborate experiments he has carried on, either in conjunction with M. Naudin on CucurbitaecEC, or by himself on fruit-trees and others, have induced him considerably to modify his former opinions. He has several times stated, both publicly and privately, that if he had to rehandlc the Plantagineae, which he had described for the Prodromus, he would find himself obliged to reduce a large proportion of the species he then adopted, and he now boldly asserts his conviction that all European Pear trees, wild or cultivated, are descended from a common stock ; this single species ever producing an infinity of seedlings, which differ so much from their original parents and from each other, in habit, constitution, foliage, flowers, or fruit, that no botanist had hitherto ventured to unite them all under one common species.

For the purpose of the elaborato pomological work he is engaged in, M. Decaisne spared no pains in collecting accurate drawings and specimens of as many forms of the Pear tree as came within his reach, and he applied himself assiduously to the distributing them into groups corresponding to supposed species, at first with some hopes of success, but, as he proceeded, he became gradually convinced, that whatever characters wore selected, the extreme forms were connected by innumerable and insensible gradations, so variously combined as to render every attempt at classification purely artificial. And wo must admit, that the doubts we ourselves expressed to him of the identity he asserted of some continental species we had believed in, were removed by the specimens and drawings he showed us, exhibiting a gradual passage from the stunted, spinescent, narrow-leaved, hoary Pyrits amygdaliformu of the limestone wastes of the south, to the lofty, elegant, broad-leaved, deep-green trees of our northern orchards; from the broadly-rounded petals, fully an inch in diameter, of the Catillac, the Saint-Gall, and others, to the oval or lanceolate petals, scarcely half an inch long, of the Heric, Sylvange, Portunee, etc.; and in the fruit, every intermediate in size, from that of a pea in Pyrus longipes, or in P. azarolifer, to that of a melon in the Poire d'Amour and de Livre (the one from 1200 to 1500 times the size of the other), and in shape, from the extremely attenuated Poire Musette, to the depressed form of some of the Bergamots and other so-called apple-shaped pears. M. Decaisne believes, indeed, that the only useful arrangement is according to the period of maturity, which, from its vagueness alone, can never be taken to be of specific value. "Ni la forme des fruits," he adds " ni leur volume, ni leur coloris, ni leur saveur, pas plus que le port et le fades des arbres, la couleur du bois, la grandeur du feuillage et des fleurs, etc. ne peuvent fournir des bases a une classification, parceque tous ces caracteres sont purement individuels,qu'il8 ne se transmettent pas fidelemeut par la voie de geeration et qu'il n'est pas meme sans exemplo qu'ils s'alterent sur un seul et meme individu, par le fait de cireonstanees locales qu'on ne peut pas toujours expliquer." The objection that these puzzling complications may be due to the innumerable hybrids arisen from the crossing of species originally distinct, is answered by the fact of the constant and perfect fertility of these crosses, whicli is always considered as evidence in favour of the specific identity of the parents.

» "With a view to practically testing the conclusions he has been led to by observation and study, M. Decaisne, in 1S53, sowed a large quantity of pear pips, taken from four varieties, considered by cultivators as amongst the most distinct, the common Parisian Poire d'Angleterre, the elongated Poire Bosc, the rounded Poire Belle Alliance, and the wild, or half wild, Poire Sauger; for the latter kind, taking the whole of the pips produced by an isolated tree on the road from Marcoussis to the Gue, near Paris. All came up the same year, except the Poire d'Angleterre, which, at two different sowings, in 1853 and 1854, only germinated the second year. Up to 18(32 only a small nnmber of these seedlings had fruited, but amongst those which had, the Poire d'Angleterre had produced six varieties, the Poire Bosc three, the Belle Alliance nine, and the Sauger four, all differing, in this the first generation, from each other, as well as from the parent, in size, form, colour, or period of maturity, besides presenting much diversity in the whole of the seedlings in habit and foliage. Varieties had thus arisen directly from one parent, which, according to the principles laid down by M. Jordan, and even of others of less extreme views, would be considered as perfectly distinct species. These results are, perhaps, no more than what have been obtained in a general way by numerous raisers of new fruits since the dayB of Mr. Knight, but they acquire importance from the precision given to them under the hands of M. Decaisne, whose detailed account must have great weight with those who are still disposed to maintain the specific immutability of small differences.

But, if the conclusions thus drawn by M. Decaisne, from his observations, supported by extraneous evidence, in so far as they are affirmative, may be considered as well established, we cannot but think that some of his negative propositions are rather hasty generalisations upon insufficient data. We believe him to have satisfactorily proved that all our cultivated pears have a common origin with our wild or Iron pear tree, and, from analogy, we may conclude with him, that P. amygdaliformis, P. Polheria, and P. salvifolia, and several other long-established indigenous European or N. Asiatic forms are conspecific, and that thus specific variation is proved in pears, as he and Naudin had previously shown it in Cucurbitacew, to be far greater than had ever been supposed. But his assertion, for instance, that this variability is so great in constitution, that whilst all varieties will graft readily on their own stock, some, such as the Poire de Eance, Clairgeau, etc., will never take if grafted on the quince, is contradicted by M. Laujoulet, a large fruit-grower, who states (" Eevue Horticole," 1803, p. 298), that he has now a row of about 400 of the Clairgeau grafted on quince, remarkable for the abundance of their fruit, and the vigour of their vegetation. His opinion is, that success or failure of grafts upon quince depends upon soil, not upon variety. We have, at present, no means of judging what weight is to be attached to his observations.

A much more important negative generalisation is that of the non-reversion of cultivated varieties to the wild type. This perfectly coincides with the opinions of many careful observers and eminent physiologists, but we can scarcely admit of its being as yet sufficiently demonstrated, nor indeed as having any very essential bearing on the great question of the derivative origin of modern species. Eeplying to the opinion of Van Mons, supported by that of many cultivators, that the seeds of good fruits will produce wild varieties (sauvageons) with acrid fruits, thus returning to what are supposed to be specific types, M. Decaisne says: "On peut tenir pour certain que toute variety distinguee de Poirier, et je dirai meme de tous nos arbres a fruits, si elle n'est fecondee que par elle-mSme, donnera saissance a de bons fruits; ik pourront differer, et differeront meme probablement, tantot par un caracttire, tantdt par un autre, de la variete' meme, mais aucun ne prendra les caracteres du sauvageon, pas plus que nos Melons-Cantaloups ne reprennent par le semis les formes, la taille et la saveur des petits Melons sauvages de l'lnde, ou que nos Choux-Cabus ou nos Choux-Fleurs ne retournent a quelqu'une de ces especes sauvages si differentes de port qui croissent But les falaises de 1'Ocean ou de la Mediterranee."

"We do not absolutely deny this proposition, for we have no convincing evidence to the contrary, but we think it very far from being proved either by M. Decaisne's experiments, or by any indis-' putable facts adduced in its favour. The varieties of fruits and vegetables gradually selected for cultivation, have been generally those whose constitution was adapted for taking advantage of the stimulants and protection of cultivation, to acquire repletion in the particular organs required for use—in the pericarp of pears, in the foliage of drum-cabbages, in the root of carrots, etc.—for being thus improved in a horticultural sense, whilst they have, generally speaking, degenerated in a physiological sense; for these varieties are msually less hardy, that is, less suited for resisting those causes of destruction which they have to contend with in a wild state. By rearing their seed in cultivated ground, circumstances are continued the most likely to foster their plethoric tendency, and the least likely to promote a recovery of their original more meagre, but more hardy constitution. If, therefore, no such tendency is observed in the offspring of a first generation, it does appear to be a hasty conclusion, that there would be no such return in the course of several generations, reared under the conditions in which the wild forms are placed. The process by which changes in the races of long-lived plants are produced in nature, are too slow to be proved by personal observation: we necessarily argue in their case from circumstantial evidence, and this evidence can only be corroborated by actual experiment upon races in which we can observe a series of successive generations. Except in the case of sudden physical changes, such as the destruction of a wood, the burning of a heath, the drainage of a lake, the laying bare of a large extent of soil by artificial cuttings or embankments, or by natural inundations, etc., thousands, not to say N. H. R.-1864. F

tens of thousands, of seeds must be scattered to waste for every single seedling that comes to perfection, under all the causes of destruction they are exposed to. Any experiments therefore which can be at all conclusive, as to whether cultivated varieties will without hybridity revert to their natural forms in the course of successive generations must be made upon annuals, or others which seed abundantly at a very early age. These must be sown in great profusion, in localities as nearly as possible similar to those which the wild types affect, yet where those types do not already exist; no cultivation must be given them beyond protection from mechanical injury, (such as being cut down, eaten up, rooted out, etc.) and assistance in dispersing their seeds every succeeding year. It will then be seen, whether after several generations the few survivors be those which havo retained the characters of their originally cultivated parents, or whether they will not be such as have degenerated from their horticultural plethora, but improved in physiological hardihood, returning as to external characters to within those limits of variation of the wild type. Circumstantial evidence is believed by M. Decaisno, as well as by others, to bo against the latter conclusion, but as yet very little of such evidence has been collected, and what has come within our own^ observation appears to us on the contrary to be in its favour. Even amongst Pear trees, a careful study of the localities of the Iron pear tree, aa observed by the most accurate of our local botanists, such, for instance, as the late Dr. Bromfield (PI. Vect. p. 164), as well as by our own experience in this country as on the Continent, would lead us to conclude that the majority at least of the supposed indigenous trees are descendants from cultivation. Moreover, if we correctly understand M. Dccaisne's expressions (p. 5 of his Memoire), several of his seedlings of cultivated varieties were thorny, which is so far a reversion, and he also states that one of his seedlings from the Sauger, the nearest to the wild pear, and one from the Bosc, the most different from it in the elongated form of the pear, produced fruits so similar to each other, as to be considered identical, which if in the one case it was a departure from the wild type, was in the other an approach towards it. Again, the wild vine trailing over the hedges and thickets of the south of France and northern Italy, which in its slender branches and small, sour berries assimilates to the supposed indigenous vine of countries further south and east, is nevertheless universally believed to bo the descendant of the

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