ON THE EXPOSURE OF PLANTS. 101 



tendency to accomodate themselves to foreign climates, or to the 

 changes of temperature of their own native place, so plants may 

 m like manner be susceptible of physical changes which would 

 enable them to bear great diversity of climatal temperature; but 

 from all experience on this point it appears, from many tropical 

 annuals long cultivated in Britain, that they have not perceptibly 

 advanced in hardihood since the first day of their introduction. 

 Such are the runner kidney-bean (which, by the bye, is a peren- 

 nial); the potato and cucumber among culinary vegetables ; the 

 China aster and balsam among flowers, and the melon among 

 fruits. All these have been perpetuated by seeds that have been 

 produced, ever since their first introduction into this country, but 

 without gaining any additional protective habit against frost. We 

 may, therefore, conclude that plants generally have been formed 

 for the climates to which they are indigenous, and have not that 

 mutability of structure or of sap which would render them invul- 

 nerable to frost in a colder country, or to the incessant excite- 

 ment of a warmer one without deterioration. 



That many plants are now seen in the open air which were for- 

 merly in the greenhouse, or even in the stove is well known; but 

 this has not happened in consequence of any change in the con- 

 atitution of those plants, but merely from being misplaced on 

 their first introduction for want of experience :-Aucuba Japonica, 

 one of our hardiest shrubs, was once under my care in the warm- 

 est end of a conservatory ! 



The effect of frost on tender vegetable bodies is mitigated by 

 thawing it off with water before the sun shines upon them. This 

 seems to contradict what has been before stated, as to dryness 

 being a safeguard to plants. But the cases are different ; perfect 

 dryness is a security against frost, but when plants are loaded 

 with frozen dew, and this allowed to be dissolved by the sun a 

 much more intense degree of cold is generated during the so- 

 lution of the icy particles by the sun, than if they were suddenly 

 dissolved by water. It is this increased degree of cold which 

 ruptures the delicate vessels of the plants, and of course destroys 

 them. J 



Sometimes we see the stem of a tender shrub, as a heath for 

 instance, rent into many pieces, whilst the youngest shoots' re 

 mam unhurt This is owing to the rigidity of the first, and the 

 dastictexture-of the second; the latter yields to the distending 

 effects ol the concealed sup, and afterwards returns to a healthy 



