3T0 SCIENCE OF AGRICULTURE. Part II. 



tables, mid some, also, on their habitation. The FCingi do not require the usual inter- 

 vention of day, in order to decompose carbonic acid gas, and can live and thrive with 

 little or no Hght. In green plants, which require the action of light, the intensity 

 requisite is very different in different species ; some require shady places, and hence the 

 vegetable inhabitants of caves, and the plants which grow in the shades of forests ; others, 

 and the greater number, require the direct action of the sun, and grow in exposed, 

 elevated sites. Decandolle considers that the great difficulty of cultivating alpine plants 

 in the gardens of plains, arises from the impossibility of giving them at once the fresh 

 temperature and intense light which they find on high mountains. 



Sect. III. Civil Causes affecting the Distribution of Plants. 



1763. By the art of man plants may he inured to circumstances foreign from tfieir usual 

 habits. Though plants in general are limited to certain habitations destined for them by 

 nature, yet some are, and probably the greater number may be, inured to climates, soils, 

 and situations, of which they are not indigenous. The means used are acclimation and 

 culture. 



1764. Acclimation seems to be most easily effected in going from a hot to a cold 

 climate, particularly with herbaceous plants ; because it often happens that the frosts of 

 winter are accompanied with snow, which shelters the plant from the inclemency of the 

 atmosphere till the return of spring. Trees and shrubs, on the contrary, are acclimated 

 with more difficulty, because they cannot be so easily sheltered from the colds, owing to 

 the greater length of their stems and branches. The acclimation, or naturalisation of 

 vegetables has been attempted by two modes : by sowing the seeds of successive gener- 

 ations, and by the difference of temperature produced by different aspects. But though 

 the habits of individuals may be altered by what is called acclimation, that is, by dimi- 

 nishing or increasing the supplies of nourishment and of heat, yet no art or device of man 

 will alter the nature of the species. The potato, the kidneybean, the nasturtium, 

 georgina, and many other plants which have been long in culture in Europe, and pro- 

 pagated from seeds ripened there through innumerable generations, there is no reason to 

 suppose are in the least degree more hardy than when first imported from Asia or South 

 America. The same slight degree of autumnal frost blackens their leaves, and of spring 

 cold destroys their germinating seeds. But as summer is nearly the same thing in all 

 lands, the summer or annual plants of the tropics are made to grow in the summers of 

 the temperate zones, and, indeed, in general, the summer plants of any one country will 

 grow in the summer climate of any other. The cucumber is grown in the fields in 

 Egypt, and near Petersburg. 



1765. Domesticated plants. " Some plants," Humboldt observes, "which constitute 

 the object of gardening and of agriculture, have time out of mind accompanied man 

 from one end of the globe to the other. In Europe the vine followed the Greeks ; the 

 wheat, the Romans ; and the cotton, the Arabs. In America, the Tultiques carried 

 with them the maize; and the potato and quinoa (Chenopodium Quinba, of which the 

 seeds are used) are found wherever have migrated the ancient Condinamarea. The 

 migration of these plants is evident ; but their first country is as little known as that of 

 the different races of men, which have been found in all parts of the globe from the 

 earliest traditions." (Gtographie des Plantes, p. 25.) 



1766. The general effect of culture on plants is that of enlarging all their parts; but 

 it often also alters the qualities, forms, and colours : it never, however, alters their pri- 

 mitive structure. " The potato," as Humboldt observes, " cultivated in Chile, at nearly 

 twelve thousand feet above the level of the sea, carries the same flower as in Siberia." 



1767. The culinary vegetables of our gardens, compared with the same species in their 

 wild state, afford striking proofs of the influence of culture on both the magnitude and 

 qualities of plants. Nothing in regard to magnitude is more remarkable than in the case 

 of the J5r^\ssica tribe ; and nothing, in respect to quality, exceeds the change effected on 

 the celery, the carrot, and the lettuce. 



1768. The influence of culture on fruits is not less remarkable. The peach, in its wild 

 state in Media, is poisonous ; but cultivated in the plains of Ispahan and Egypt, it 

 becomes one of the most delicious of fruits. The effect of culture on the apple, pear, 

 cherry, plum, and other fruits, is nearly as remarkable ; for not only the fruit and leaves, 

 but the general habits of the tree, are altered in these and other species. The history of 

 the migration of fruit trees has been commenced by Sickler, in a work (Geschichte, &c.) 

 which Humboldt has praised as equally curious and philosophical. 



1769. The influence of culture on plants of ornament is great in most species. The 

 parts of all plants are enlarged ; some are numerically increased, as in the case of double 

 flowers ; and, what is most remarkable, even the colours are frequently changed, in the 

 leaf, flower, and fruit. 



1770. The influence of civilisation and culture, in increasing the number of plants in a 

 country, is very considerable, and operates directly, by introducing new species for cul- 



