clapping of hands, but this distinction in the usage of the words is by no means uniformly maintained. Among the Romans acclamation was varied both in form and purpose. At marriages it was usual for the spectators to shout Io Hymen, Hymenae, or Talassio; a victorious army or general was greeted with Io triumphe; in the theatre acclamation was called for at the close of the play by the last actor, who said, Plaudite; in the senate opinions were expressed and votes passed by acclamation in such forms as Omnes, omnes, Equum est, Justum est, &c; and the praises of the emperor were celebrated in certain pre-arranged sentences, which seem to have been chanted by the whole body of senators. The acclamations which authors and poets who recited their works in public received were at first spontaneous and genuine, but in time became very largely mercenary, it being customary for men of fortune who affected literary tastes to keep applauders in their service and lend them to their friends. When Nero performed in the theatre his praises were chanted, at a given signal, by five thousand soldiers, who were called Augustals. The whole was conducted by a music-master, mesochorus or pausarius. It was this case of Nero which, occurring to the recollection of the French poet Dorat, may be said to have originated the well-known Paris claque. Buying up a number of the tickets for a performance of one of his plays, he distributed them gratuitously to those who promised to express approbation. From that time the claque, or organised body of professional applauders, has been a recognised institution in connection with the theatres of Paris. In the early ages of the Christian church it was by no means uncommon for an audience to express their approbation of a favourite preacher during the course of his sermon. Chrysostom especially was very frequently interrupted both by applause and by acclamations. In ecclesiastical councils vote by acclamation is very common, the question being usually put in the form, placet or non placet. This differs from the acclamation with which in other assemblies a motion is said to be carried, when, no amendment being proposed, approval is expressed by shouting such words as Aye or Agreed.

ACCLIMATISATION is the process of adaptation by which animals and plants are gradually rendered capable of surviving and flourishing in countries remote from their original habitats, or under meteorological conditions dif ferent from those which they have usually to endure, and which are at first injurious to them.

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The subject of acclimatisation is very little understood, and some writers have even denied that it can ever take place. It is often confounded with domestication or with naturalisation; but these are both very different phenoA domesticated animal or a cultivated plant need not necessarily be acclimatised; that is, it need not be capable of enduring the severity of the seasons without protection. The canary bird is domesticated but not acclimatised, and many of our most extensively cultivated plants are in the same category. A naturalised animal or plant, on the other hand, must be able to withstand all the vicissitudes of the seasons in its new home, and it may therefore be thought that it must have become acclimatised. But in many, perhaps most cases of naturalisation, there is no evidence of a gradual adaptation to new conditions which were at first injurious, and this is essential to the idea of acclimatisation. On the contrary, many species, in a new country and under somewhat different climatic conditions, seem to find a more congenial abode than in their native land, and at once flourish and increase in it to such an extent as often to exterminate the indigenous inhabitants. Thus Agassiz (in his work on Lake Superior) tells us that the road-side weeds of the north-eastern United States, to the number of 130 species, are all European, the native weeds having dis

appeared westwards; while in New Zealand there are, according to Mr T. Kirk (Transactions of the New Zealand Institute, vol. ii. p. 131), no less than 250 species of naturalised plants, more than 100 of which spread widely over the country, and often displace the native vegetation. Among animals, the European rat, goat, and pig, are naturalised in New Zealand, where they multiply to such an extent as to injure and probably exterminate many native productions. In neither of these cases is there any indication that acclimatisation was necessary or ever took place.

On the other hand, the fact that an animal or plant cannot be naturalised is no proof that it is not acclimatised. It has been shown by Mr Darwin that, in the case of most animals and plants in a state of nature, the competition of other organisms is a far more efficient agency in limiting their distribution than the mere influence of climate. We have a proof of this in the fact that so few, comparatively, of our perfectly hardy garden plants ever run wild; and even the most persevering attempts to naturalise them usually fail. Alphonse de Candolle (Géographie Botanique, p. 798) informs us that several botanists of Paris, Geneva, and especially of Montpellier, have sown the seeds of many hundreds of species of exotic hardy plants, in what appeared to be the most favourable situations, but that in hardly a single case has any one of them become naturalised. Attempts have also been made to naturalise continental insects in this country, in places where the proper foodplants abound and the conditions seem generally favourable, but in no case do they seem to have succeeded. Even a plant like the potato, so largely cultivated and so perfectly hardy, has not established itself in a wild state in any part of Europe.

Different Degrees of Climatal Adaptation in Animals and Plants.-Plants differ greatly from animals in the closeness of their adaptation to meteorological conditions. Not only will most tropical plants refuse to live in a temperate climate, but many species are seriously injured by removal a few degrees of latitude beyond their natural limits. This is probably due to the fact, established by the experiments of M. Becquerel, that plants possess no proper temperature, but are wholly dependent on that of the surrounding medium.

Animals, especially the higher forms, are much less sensitive to change of temperature, as shown by the extensive range from north to south of many species. Thus, the tiger ranges from the equator to northern Asia as far as the river Amour, and to the isothermal of 32° Fahr. The mountain sparrow (Passer montana) is abundant in Java and Singapore in a uniform equatorial climate, and also inhabits this country and a considerable portion of northern Europe. It is true that most terrestrial animals are restricted to countries not possessing a great range of temperature or very diversified climates, but there is reason to believe that this is due to quite a different set of causes, such as the presence of enemies or deficiency of appropriate food. When supplied with food and partially protected from enemies, they often show a wonderful capacity of enduring climates very different from that in which they originally flourished. Thus, the horse and the domestic fowl, both natives of very warm countries, flourish without special protection in almost every inhabited portion of the globe. The parrot tribe form one of the most pre-eminently tropical groups of birds, only a few species extending into the warmer temperate regions; yet even the most exclusively tropical genera are by no means delicate birds as regards climate. In the Annals and Magazine of Natural History for 1868 (p. 381) is a most interesting account, by Mr Charles Buxton, M.P., of the naturalisation of parrots at Northreps Hall, Norfolk. A considerable number of

African and Amazonian parrots, Bengal parroquets, four species of white and rose crested cockatoos, and two species of crimson lories, have been at large for many years. Several of these birds have bred, and they almost all live in the woods the whole year through, refusing to take shelter in a house constructed for their use. Even when the thermometer fell 6° below zero, all appeared in good spirits and vigorous health. Some of these birds have lived thus exposed for nearly twenty years, enduring our cold easterly winds, rain, hail, and snow, all through the winter,—a marvellous contrast to the equable equatorial temperature (hardly ever less than 70°) which many of them had been accustomed to for the first year or years of their existence.

Mr Jenner Weir records somewhat similar facts in the Zoologist for 1865 (p. 9411). He keeps many small birds in an open aviary in his garden at Blackheath, and among these are the Java rice bird (Padda oryzivora), two West African weaver birds (Hyphantornis textor and Euplectes sanguinirostris), and the blue bird of the southern United States (Spiza cyanea). These denizens of the tropics prove quite as hardy as our native birds, having lived during the severest winters without the slightest protection against the cold, even when their drinking water had to be repeatedly melted.

Hardly any group of Mammalia is more exclusively tropical than the Quadrumana, yet there is reason to believe that, if other conditions are favourable, some of them can withstand a considerable degree of cold. The Semnopithecus schistaceus was found by Captain Hutton at an elevation of 11,000 feet in the Himalayas, leaping actively among firtrees whose branches were laden with snow-wreaths. In Abyssinia a troop of dog-faced baboons were observed by Mr Blandford at 9000 feet above the sea. We may therefore conclude that the restriction of the monkey tribe to warm latitudes is probably determined by other causes than temperature alone.

Similar indications are given by the fact of closely allied species inhabiting very extreme climates. The recently extinct Siberian mammoth and woolly rhinoceros were closely allied to species now inhabiting tropical regions exclusively. Wolves and foxes are found alike in the coldest and hottest parts of the earth, as are closely allied species of falcons, owls, sparrows, and numerous genera of waders and aquatic birds.

A consideration of these and many analogous facts might induce us to suppose that, among the higher animals at least, there is little constitutional adaptation to climate, and that in their case acclimatisation is not required. But there are numerous examples of domestic animals which show that such adaptation does exist in other cases. The yak of Thibet cannot long survive in the plains of India, or even on the hills below a certain altitude; and that this is due to climate, and not to the increased density of the atmosphere, is shown by the fact that the same animal appears to thrive well in Europe, and even breeds there readily. The Newfoundland dog will not live in India, and the Spanish breed of fowls in this country suffer more from frost than most others. When we get lower in the scale the adaptation is often more marked. Snakes, which are so abundant in warm countries, diminish rapidly as we go north, and wholly cease at lat. 62°. Most insects are also very susceptible to cold, and seem to be adapted to very narrow limits of temperature.

From the foregoing facts and observations we may conlude, firstly, that some plants and many animals are not constitutionally adapted to the climate of their native country only, but are capable of enduring and flourishing under a more or less extensive range of temperature and other climatic conditions; and, secondly, that most plants

and some animals are, more or less closely, adapted to climates similar to those of their native habitats. In order to domesticate or naturalise the former class in countries not extremely differing from that from which the species was brought, it will not be necessary to acclimatise, in the strict sense of the word. In the case of the latter class, however, acclimatisation is a necessary preliminary to naturalisation, and in many cases to useful domestication, and we have therefore to inquire whether it is possible.

Acclimatisation by Individual Adaptation.-It is evident that acclimatisation may occur (if it occurs at all) in two ways, either by modifying the constitution of the individual submitted to the new conditions, or by the production of offspring which may be better adapted to those conditions than their parents. The alteration of the constitution of individuals in this direction is not easy to detect, and its possibility has been denied by many writers. Mr Darwin believes, however, that there are indications that it occasionally occurs in plants, where it can be best observed, owing to the circumstance that so many plants are propagated by cuttings or buds, which really continue the existence of the same individual almost indefinitely. He adduces the example of vines taken to the West Indies from Madeira, which have been found to succeed better than those taken directly from France. But in most cases habit, however prolonged, appears to have little effect on the constitution of the individual, and the fact has no doubt led to the opinion that acclimatisation is impossible. There is indeed little or no evidence to show that any animal to which a new climate is at first prejudicial can be so acclimatised by habit that, after subjection to it for a few or many seasons, it may live as healthily and with as little care as in its native country; yet we may, on general principles, believe that under proper conditions such acclimatisation would take place. In his Principles of Biology (chap. v.), Mr Herbert Spencer has shown that every organ and every function of living beings undergoes modification to a limited extent under the stimulus of any new conditions, and that the modification is almost always such as to produce an adaptation to those conditions. We may feel pretty sure, therefore, that if robust and healthy individuals are chosen for the experiment, and if the change they are subjected to is not too great, a real individual adaptation to the new conditions-that is, a more or less complete acclimatisation-will be brought about. If now animals thus modified are bred from, we know that their descendants will inherit the modification. They will thus start more favourably, and being subject to the influence of the same or a slightly more extreme climate during their whole lives, the acclimatisation will be carried a step further; and there seems no reason to doubt that, by this process alone, if cautiously and patiently carried out, most animals which breed freely in confinement could in time be acclimatised in almost any inhabited country. There is, however, a much more potent agent, which renders the process of adaptation almost a certainty.

Acclimatisation by Variation.—A mass of evidence exists showing that variations of every conceivable kind occur among the offspring of all plants and animals, and that, in particular, constitutional variations are by no means uncommon. Among cultivated plants, for example, hardier and more tender varieties often arise. The following cases are given by Mr Darwin :-Among the numerous fruit-trees raised in North America, some are well adapted to the climate of the Northern States and Canada, while others only succeed well in the Southern States. Adaptation of this kind is sometimes very close, so that, for example, few English varieties of wheat will thrive in Scotland. Seedwheat from India produced a miserable crop when planted

species or closely allied forms inhabiting the surrounding islands; the species found in Celebes possess a peculiar form of wing, quite distinct from that of the same or closely allied species of adjacent islands; and, lastly, numerous species which have tailed wings in India and the western islands of the Archipelago, gradually lose the tail as we proceed eastward to New Guinea and the Pacific. Many of these curious modifications may, it is true, be due to other causes than climate only, but they serve to show how powerfully and mysteriously local conditions affect the form and structure of both plants and animals; and they render it probable that changes of constitution are also continually produced, although we have, in the majority of cases, no means of detecting them. It is also impossible to determine how far the effects described are produced by spontaneous favourable variations or by the direct action of local conditions; but it is probable that in every case both causes are concerned, although in constantly varying proportions.

The

The Influence of Heredity.-Adaptation by variation. would, however, be a slow and uncertain process, and might for considerable periods of time cease to act, did not heredity come into play. This is the tendency of every organism to produce its like, or more exactly, to produce a set of new forms varying slightly from it in many directions-a group of which the parent form is the centre. If now one of the most extreme of these variations is taken, it is found to become the centre of a new set of variations; and by continually taking the extreme in the same direction, an increasing variation in that direction can be effected, until checked by becoming so great that it interferes with the healthy action of the organism, or is in any other way prejudicial. It is also found that acquired constitutional peculiarities are equally hereditary; so that by a combination of those two modes of variation any desired adaptation may be effected with greater rapidity. The manner in which the form or constitution of an organism can be made to change continuously in one direction, by means of variations which are indefinite and in all directions, is often misunderstood. It may perhaps be illustrated by showing how a tree or grove of trees might, by natural causes, be caused to travel during successive generations in a definite course. tree has branches radiating out from its stem to perhaps twenty feet on every side. Seeds are produced on the extremities of all these branches, drop to the ground, and produce seedlings, which, if untouched, would form a ring of young trees around the parent. But cattle crop off every seedling as soon as it rises above the ground, and none can ever arrive at maturity. If, however, one side is protected from the cattle, young trees will grow up on that side only. This protection may exist in the case of a grove of trees which we may suppose to occupy the whole space between two deep ravines, the cattle existing on the lower side of the wood only. In this case young trees would reach maturity on the upper side of the wood, while on the lower side the trees would successively die, fall, and rot away, no young ones taking their place. If this state of things continued unchanged for some centuries, the wood might march regularly up the side of the mountain till it occupied a position many miles away from where it once stood; and this would have taken place, not because more seed was produced on one side than the other (there might even be very much less), nor because soil or climate were better on the upper side (they might be worse), nor because any intelligent being chose which trees should be allowed to live and which should be destroyed;--but simply because, for a series of generations, the conditions permitted the existence of young trees on one side, and wholly prevented it on the other. Just in an analogous way animals or plants are caused to vary in definite directions, either by

the influence of natural agencies, which render existence impossible for those that vary in any other direction, or by the action of the judicious breeder, who carefully selects favourable variations to be the parents of his future stock; and in either case the rejected variations may far outnumber those which are preserved.

Evidence has been adduced by Mr Darwin to show that the tendency to vary is itself hereditary; so that, so far from variations coming to an end, as some persons imagine, the more extensively variation has occurred in any species in the past, the more likely it is to occur in the future. There is also reason to believe that individuals which have varied largely from their parents in a special direction will have a greater tendency to produce offspring varying in that direction than in any other; so that the facilities for adaptation, that is, for the production and increase of favourable variations in certain definite directions, are far greater than the facilities for locomotion in one direction in the hypothetical illustration just given.

Selection and Survival of the Fittest as Agents in Naturalisation.-We may now take it as an established fact, that varieties of animals and plants occur, both in domesticity and in a state of nature, which are better or worse adapted to special climates. There is no positive evidence that the influence of new climatal conditions on the parents has any tendency to produce variations in the offspring better adapted to such conditions, although some of the facts mentioned in the preceding sections render it probable that such may be the case. Neither does it appear that this class of variations are very frequent. It is, however, certain that whenever any animal or plant is largely propagated constitutional variations will arise, and some of these will be better adapted than others to the climatal and other conditions of the locality. In a state of nature, every recurring severe winter or otherwise unfavourable season, weeds out those individuals of tender constitution or imperfect structure which may have got on very well during favourable years, and it is thus that the adaptation of the species to the climate in which it has to exist is kept up. Under domestication the same thing occurs by what Mr Darwin has termed "unconscious selection." Each cultivator seeks out the kinds of plants best suited to his soil and climate, and rejects those which are tender or otherwise unsuitable. The farmer breeds from such of his stock as he finds to thrive best with him, and gets rid of those which suffer from cold, damp, or disease. A more or less close adaptation to local conditions is thus brought about, and breeds or races are produced which are sometimes liable to deterioration on removal even to a short distance in the same country, as in numerous cases quoted by Mr Darwin (Animals and Plants under Domestication, vol. ii. p. 273).

The Method of Acclimatisation.-Taking into consideration the foregoing facts and illustrations, it may be considered as proved-1st, That habit has little (though it appears to have some) definite effect in adapting the constitution of animals to a new climate; but that it has a decided, though still slight, influence in plants when, by the process of propagation by buds, shoots, or grafts, the individual can be kept under its influence for long periods; 2d, That the offspring of both plants and animals vary in their constitutional adaptation to climate, and that this adaptation may be kept up and increased by means of heredity; and, 3d, That great and sudden changes of climate often check reproduction even when the health of the individuals does not appear to suffer. In order, therefore, to have the best chance of acclimatising any animal or plant in a climate very dissimilar from that of its native country, and in which it has been proved that the species in question cannot live and maintain itself

1. We must transport as large a number as possible of adult healthy individuals to some intermediate station, and increase them as much as possible for some years. Favourable variations of constitution will soon show them selves, and these should be carefully selected to breed from, the tender and unhealthy individuals being rigidly eliminated.

2. As soon as the stock has been kept a sufficient time to pass through all the ordinary extremes of climate, a number of the hardiest may be removed to the more remote station, and the same process gone through, giving protection if necessary while the stock is being increased, but as soon as a large number of healthy individuals are produced, subjecting them to all the vicissitudes of the climate.

It can hardly be doubted that in most cases this plan would succeed. It has been recommended by Mr Darwin, and at one of the early meetings of the Société Zoologique d'Acclimatisation, at Paris, M. Geoffroy St Hilaire insisted that it was the only method by which acclimatisation was possible. But in looking through the long series of volumes of Reports published by this Society, there is no sign that any systematic attempt at acclimatisation has even once been made. A number of foreign animals have been introduced, and more or less domesticated, and some useful exotics have been cultivated for the purpose of testing their applicability to French agriculture or horticulture; but neither in the case of animals nor of plants has there been any systematic effort to modify the constitution of the species, by breeding largely and selecting the favourable variations that appeared.

Take the case of the Eucalyptus globulus as an example. This is a Tasmanian gum-tree of very rapid growth and great beauty, which will thrive in the extreme south of France. In the Bulletin of the Society a large number of attempts to introduce this tree into general cultivation in other parts of France are recorded in detail, with the failure of almost all of them. But no precautions such as those above indicated appear to have been taken in any of these experiments; and we have no intimation that either the Society or any of its members are making systematic efforts to acclimatise the tree. The first step would be, to obtain seed from healthy trees growing in the coldest climate and at the greatest altitude in its native country, sowing these very largely, and in a variety of soils and situations, in a part of France where the climate is somewhat but not much more extreme. It is almost a certainty that a number of trees would be found to be quite hardy. As soon as these produced seed, it should be sown in the same district and farther north in a climate a little more severe. After an exceptionally cold season, seed should be collected from the trees that suffered least, and should be sown in various districts all over France. By such a process there can be hardly any doubt that the tree would be thoroughly acclimatised in any part of France, and in many other countries of central Europe; and more good would be effected by one well-directed effort of this kind than by hundreds of experiments with individual animals and plants, which only serve to show us which are the species that do not require to be acclimatised.

Acclimatisation of Man.-On this subject we have, unfortunately, very little direct or accurate information. The general laws of heredity and variation have been proved to apply to man as well as to animals and plants; and numerous facts in the distribution of races show that man must, in remote ages at least, have been capable of constitutional adaptation to climate. If the human race constitutes a single specics, then the mere fact that man now inhabits every region, and is in each case constitutionally adapted to the climate, proves that acclimatisation has occurred. But we

the American, which inhabits alike the frozen wastes of Hudson's Bay and Terra del Fuego, and the hottest regions of the tropics, the low equatorial valleys and the lofty plateaux of the Andes. No doubt a sudden transference to an extreme climate is often prejudicial to man, as it is to most animals and plants; but there is every reason to believe that, if the migration occurs step by step, man can be acclimatised to almost any part of the earth's surface in comparatively few generations. Some eminent writers have denied this. Sir Ranald Martin, from a consideration of the effects of the climate of India on Europeans and their offspring, believes that there is no such thing as acclimatisation. Dr Hunt, in a report to the British Association in 1861, argues that "time is no agent,” and "if there is no sign of acclimatisation in one generation, there is no such process." But he entirely ignores the effect of favourable variations, as well as the direct influence of climate acting on the organisation from infancy. Professor Waitz, in his Introduction to Anthropology, adduces many examples of the comparatively rapid con stitutional adaptation of man to new climatic conditions. Negroes, for example, who have been for three or four generations acclimatised in North America, on returning to Africa become subject to the same local diseases as other unacclimatised individuals. He well remarks, that the debility and sickening of Europeans in many tropical countries are wrongly ascribed to the climate, but are rather the consequences of indolence, sensual gratification, and an irregular mode of life. Thus the English, who cannot give up animal food and spirituous liquors, are less able to sustain the heat of the tropics than the more sober Spaniards and Portuguese. The excessive mortality of European troops in India, and the delicacy of the children of European parents, do not affect the real question of acclimatisation under proper conditions. They only show that acclimatisation is in most cases necessary, not that it cannot take place. The best examples of partial or complete acclimatisation are to be found where European races have permanently settled in the tropics, and have maintained themselves for several generations. There are, however, two sources of inaccuracy to be guarded against, and these are made the most of by the writers above referred to, and are supposed altogether to invalidate results which are otherwise opposed to their views. In the first place, we have the possibility of a mixture of native blood having occurred; in the second, there have almost always been a succession of immigrants from the parent country, who continually intermingle with the families of the early settlers. It is maintained that one or other of these mixtures is absolutely necessary to enable Europeans to continue long to flourish in the tropics.

There are, however, certain cases in which the sources of error above mentioned are reduced to a minimum, and cannot seriously affect the results; such as those of the Jews, the Dutch at the Cape of Good Hope and in the Moluccas, and the Spaniards in South America.

The Jews are a good example of acclimatisation, because they have been established for many centuries in climates very different from that of their native land; they keep themselves almost wholly free from intermixture with the people around them; and they are often so populous in a country that the intermixture with Jewish immigrants from other lands cannot seriously affect the local purity of the race. They have, for instance, attained a population of near two millions in such severe climates as Poland and Russia; and according to Mr Brace (Races of the Old World, p. 185), "their increase in Sweden is said to be greater than that of the Christian population; in the towns of Algeria they are the only race able to maintain its numbers; and in