136 SOIL OF THE ORANGE AND VINE. 



is afforded by the known degree of warmth of the climate of 

 which a plant may be a native. 



When plants are cultivated in glass houses, there is little 

 difficulty in supplying them with the amount of bottom heat 

 which they may require ; but this can either not be effected at 

 all, or only to a limited degree, by a selection of soils and situ- 

 ations, when plants are cultivated in the open air ; and hence 

 one of the many difficulties of acclimatising in a cold country 

 the species of a warmer climate. It is true that plants will exist 

 within wide limits of temperature, and, consequently, a few 

 degrees of difference in the natural bottom heat to which they 

 are exposed may not affect them so far as to destroy them ; but 

 it cannot be doubted that the conditions most favourable to 

 their growth are those which embrace a temperature rather 

 above than below that to which they are accustomed in their 

 native haunts. 



The Orange-tree is found in perfection where the tempera- 

 ture of the soil may be computed to rise to 80° or 85°, and 

 never to fall below 58°, as in the Bermudas, Malta, and Canton. 

 How injudicious, then, is our practice of exposing it during 

 summer to the open air, in tubs, where the soil scarcely rises 

 in temperature above 66°, and preserving it during winter in 

 cold conservatories, the soil of which often sinks to 36° ; under 

 such circumstances the Orange exists indeed, but where are 

 the perfume and juiciness of its fruit, and where the healthy 

 vigour of its noble foliage ? The Vine cannot be grown in the 

 open air of this country to any useful purpose, except when 

 trained to walls, in soils and situations unusually exposed to 

 the beams of the sun; it is only then that it can obtain for its 

 roots such a permanent warmth as 75° which it will have at 

 Bordea,ux, or 80° in Madeira. 



It may hence be considered an axiom in horticulture, that 

 all plants require the soil, as well as the atmosphere, in which 

 they grow, to correspond in temperature with that of the 

 countries of which they are natives. It has also been already 

 shown, that the mean temperature of the soil should be above 

 that of the atmosphere. How much above depends upon 

 climate a,nd season. The meaii difference in favour of the. 



