Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/102

Rh 86 ACCLIMATISATION by the Rev. M. J. Berkeley on land which would have produced a good crop of English wheat. Conversely, French wheat taken to the West Indies produced only barren spikes, while native wheat by its side yielded an enormous harvest. Tobacco in Sweden, raised from home grown seed, ripens its seeds a month earlier than plants grown from foreign seed. In Italy, as long as orange trees were propagated by grafts, they were tender ; but after many of the trees were destroyed by the severe frosts of 1709 and 1763, plants were raised from seed, arid these were found to be hardier and more productive than the former kinds. Where plants are raised from seed in large quantities, varieties always occur differing in constitution, as well as others differing in form or colour ; but the former cannot be perceived by us unless marked out by their behaviour under exceptional conditions, as in the following cases. After the severe winter of 1860-61, it was observed that in a large bed of araucarias some plants stood quite unhurt among numbers killed around them. In Mr Darwin s garden two rows of scarlet runners were entirely killed by frost, except three plants, which had not even the tips of their leaves browned. A very excellent example is to be found in Chinese history, according to M. Hue, who, in his UEmpire Chinois (torn. ii. p. 359), gives the following extract from the Memoirs of the Emperor Khang : &quot; On the 1st day of the 6th moon I was walking in some fields where rice had been sown to be ready for the harvest in the 9th moon. I observed by chance a stalk of rice which was already in ear. It was higher than all the rest, and was ripe enough to be gathered. I ordered it to be brought to me. The grain was very fine and well grown, which gave me the idea to keep it for a trial, and see if the following year it would preserve its precocity. It did so. All the stalks which came from it showed ear before the usual time, and were ripe in the 6th moon. Each year has multiplied the produce of the preceding, and for thirty years it is this rice which has been served at my table. The grain is elongate, and of a reddish colour, but it has a sweet smell and very pleasant taste. It is called Yu-mi, Imperial rice, because it was first cultivated in my gardens. It is the only sort which can ripen north of the great wall, where the winter ends late and begins very early ; but in the southern provinces, where the climate is milder and the land more fertile, two harvests a year may be easily ob tained, and it is for me a sweet reflection to have procured this advantage for my people.&quot; M. Hue adds his testimony that this kind of rice flourishes in Mandtchuria, where no other will grow. We have here, therefore, a perfect example of acclimatisation by means of a spontaneous con stitutional variation. That this kind of adaptation may be carried on step by step to more and more extreme climates is illustrated by the following examples. Sweet-peas raised in Calcutta from seed imported from England rarely blossom, and never yield seed ; plants from French seed flower better, but are still sterile ; but those raised from Darjeeling seed (originally imported from England) both flower and seed profusely. The peach is believed to have been tender, and to have ripened its fruit with difficulty, when first introduced into Greece; so that (as Darwin observes) in travelling northward during two thousand years it must have become much hardier. Dr Hooker ascertained the average vertical range of flowering plants in the Himalayas to be 4000 feet, while in some cases it extended to 8000 feet. The same species can thus endure a great difference of temperature ; but the important fact is, that the individuals have become accli matised to the altitude at which they grow, so that seeds gathered near the upper limit of the range of a species will be more hardy than those gathered near the lower limit. This was proved by Dr Hooker to be the case with Himalayan conifers and rhododendrons, raised in this country from seed gathered at different altitudes. Among animals exactly analogous facts occur. M. Roulin states that when geese were first introduced into Bogota they laid few eggs at long intervals, and few of the young survived. By degrees the fecundity improved, and in about twenty years became equal to what it is in Europe. The same author tells us that, according to Garcilaso, when fowls were first introduced into Peru they were not fertile, whereas now they are as much so as in Europe. Mr Darwin adduces the following examples. Merino sheep bred at the Cape of Good Hope have been found far better adapted for India than those imported from England ; and while the Chinese variety of the Ailanthus silk-moth is quite hardy, the variety found in Bengal will only flourish in warm latitudes. Mr Darwin also calls attention to the circumstance that writers of agricultiiral works generally recommend that animals should be removed from one district to another as little as possible. This advice occurs even in classical and Chinese agricultural books as well as in those of our own day, and proves that the close adaptation of each variety or breed to the country in which it originated has always been recognised. Constitutional Adaptation often accompanied by External Modification. Although in some cases no perceptible altera tion of form or structure occurs when constitutional adapta tion to climate has taken place, in others it is very marked. Mr Darwin has collected a large number of cases inhisAnimals and Plants under Domestication (vol. ii. p. 277), of which the following are a few of the most remarkable. Dr Falconer observed that several trees, natives of cooler climates, assumed a pyramidal or fastigiate form when grown in the plains of India ; cabbages rarely produce heads in hot climates ; the quality of the wood, the medicinal products, the odour and colour of the flowers, all change in many cases when plants of one country are grown in another. One of the most curious observations is that of Mr Meehan, who &quot; compared twenty-nine kinds of American tree? belonging to various orders, with their nearest European allies, all grown in close proximity in the same garden, and under as nearly as possible the same conditions. In the American species Mr Meehan finds, with the rarest excep tions, that the leaves fall earlier in the season, and assume before falling a brighter tint ; that they are less deeply toothed or serrated ; that the buds are smaller ; that the trees are more diffuse in growth, and have fewer branchlets; and, lastly, that the seeds are smaller ; all in comparison with the European species.&quot; Mr Darwin concludes thai there is no way of accounting for these uniform differences in the two series of trees than by the long-continued action of the different climates of the two continents. In animals equally remarkable changes occur. In Angora, not only goats, but shepherd-dogs and cats, have fine fleecy hair ; the wool of sheep changes its character in the West Indies in three generations ; M. Costa states that young oysters, taken from the coast of England, and placed in the Mediterranean, at once altered their manner of growth and formed prominent diverging rays, like those on the shells of the proper Mediterranean oyster. In his Contributions to the Theory of Natural Selection (p. 167), Mr Wallace has recorded cases of simultaneous variation among insects, apparently due to climate or other strictly local causes. He finds that the butterflies of the family Papilionidce, and some others, become similarly modified in different islands and groups of islands. Thus, the species inhabiting Sumatra, Java, and Borneo, are almost always much smaller than the closely allied species of Celebes and the Moluccas ; the species or varieties of the small island of Amboyna are larger than the same