794 



OPEN FLOWER-GARDEN. 



their operation in autumn, for the purpose of 

 maturing the wood, would be, of course, an 

 advantage ; heated during spring would have a 

 contrary effect. 



Altitude, as we have already stated, has also 

 much to do in the successful cultivation of exo- 

 tic trees and plants, and their preservation 

 during winter. Altitude above the sea has 

 been calculated as being equivalent, on the 

 score of climate, to a receding north or south 

 from the equator, 600 feet of altitude being 

 thought to be equal to a degree. The influence 

 of elevation above the sea-level in depressing 

 the temperature has been very little attended to 

 in Britain. Sir Thomas Brisbane and Mr Gal- 

 braith (vide " New Edinburgh Journal ") have 

 estimated the decrease to be 1° of temperature 

 for 212 feet of ascent in lat. 55°-51° ; while Mr 

 Hewett Watson (vide " Magazine of Natural 

 History") raises it to 239 feet between 53°-59°. 

 These estimates do not refer to the winter 

 months ; nor is either of them worthy of impli- 

 cit reliance. According to De CandoUe, heat 

 decreases in France at the rate of one degree of 

 latitude for every 540 feet of altitude. In the 

 middle of the temperate zone Humboldt re- 

 marked that the mean heat of the year diminished 

 at the rate of 2° north latitude for every 600 

 feet of altitude. From the powerful influence on 

 temperature produced by elevation arise those 

 discrepancies which occur in the ripening of fruits 

 and precocity of vegetation between gardens 

 near the sea-level and those at a greater altitude, 

 although at no very great distance from it. 



" The mean heat of any situation," Loudon 

 remarks, " does not enable us to judge of what 

 particular species of plants will live there ; for 

 the mean temperature found may be deduced 

 from such extremes of heat and cold as would 

 suit but few plants ; or it may be made up from 

 moderate limits, in which many plants will live; 

 as, for example, from the summers and winters of 

 Ireland, or the sea-coast of the middle of Europe. 

 Thus the constitution of a plant, which may be 

 very well suited for the mean temperature of a 

 place, may not be adapted to its extreme differ- 

 ences. Hence many plants, which will live in 

 the open air at Belfast, would perish in the 

 winters at Edinburgh ; and many which would 

 live there, owing to the dryness of the air and 

 the moderate degree of cold from the proximity 

 of the sea, would perish in Yorkshire, where the 

 air is not only more highly charged with mois- 

 ture, but much colder. Hence the mean annual 

 temperature of any place is of>much less conse- 

 quence, with respect to its influence upon plants 

 and fruit trees, than the mean monthly tem- 

 perature, and the extremes of each month." 

 The latter form the data, therefore, that culti- 

 vators ought to be guided by in determining on 

 their selections of plants and tender fruit trees. 



The most serious effects of frost on vegetable 

 bodies arise from the sap becoming frozen in 

 the vessels, which are consequently ruptured 

 by its expansion ; and therefore all soft-wooded 

 plants are much more liable to be affected by 

 intense cold than hard-wooded ones, on account 

 not only of the former being more charged 

 with sap in proportion to their bulk, but also be- 



cause their bark, or outer covering, is thinner 

 and softer, and their roots nearer the sur- 

 face. The rugged barks of hard-wooded trees 

 are powerful non-conductors ; while soft-wooded 

 plants have smooth and very thin skins, and 

 are less fortified against cold, for want of suffi- 

 cient non-conducting covering, and hence less 

 capable of resisting cold. The roots of plants, 

 such as trees, &c., which penetrate deepest into 

 the soil, are, from another cause, better able to 

 resist severe cold, because they penetrate deeper 

 into the soil than frost ; and as a slow circula- 

 tion is carried on in their trunks and branches 

 throughout the winter, the sap they contain is 

 prevented from being frozen, by the heat they ob- 

 tain from the subsoil. Hence the great advan- 

 tage of covering the soil above the roots by 

 mulching them over with litter, or some other 

 non-conducting material, to prevent the loss of 

 heat from the soil by radiation. On a similar 

 principle, the practice of covering the stem and 

 main branches, by envelopingthem in straw,moss, 

 or other covering, is advantageous, as it assists 

 the bark in resisting frost, or probably it acts 

 rather by preventing the loss of internal heat. 



Acclimatation is the doctrine of rendering 

 plants of a warmer country, by cultivation, &c., 

 capable of thriving in another which is colder. 

 On this subject opinions widely differ. The 

 advocates for it assert that the sensibility of 

 plants may be diminished in habit by a gradation 

 of climate, and by a succession of generations — 

 that is, by slight protection for a few years after 

 planting, and gradually exposing them to the 

 natural climate of our gardens, and also by rear- 

 ing plants from seed ripened in the open air of 

 our gardens. Few satisfactory instances have 

 been recorded of such effects being produced. 

 The circumstance, however, that the quality o 

 the products of many plants is greatly changed 

 by raising generation after generation from seed, 

 seems to some extent to favour this idea. That 

 a very considerable difference of constitution 

 exists among individuals of the same species is 

 undeniable, some being far more robust and 

 capable of resisting external influences than 

 others. From these seed should invariably be 

 taken. The majority of the plants and trees, 

 natives of warmer climates, which are found to 

 resist the effects of our severest winters in the 

 open air, never were tender, as may be instanced 

 in the cases of Araucaria imbricata, Aucuba ja- 

 ponica, Kerria japonica. Glycine sinensis, Wei- 

 gela rosea, &c. Whereas, on the other hand, 

 no change has been produced on the hardiness 

 of other plants much longer cultivated in our 

 gardens, and annually reproduced from seed 

 ripened in our climate, as may be exemplified 

 in the case of the tomato, kidney-bean, mignon- 

 ette, and a host of others. 



The last winter (1853-4) has been the most 

 trying for many years past. The plants which 

 have survived it in the open air may be regarded 

 as possessing a hardy constitution, compared 

 with others from the same country, and in 

 many cases of the same genus. The following 

 list of survivors, which is partly compiled from 

 the excellent article on "The Effects of the 

 Winter of 1853-4," in the " Journal of the Lon- 



