

ON THE NATURALIZATION OF PLANTS. 149 



cannot poffibly be cultivated in the interior of Afia or Ame- 

 rica, though the latitude be in other refpe&s favourable, nor 

 is it fruitful when excluded from the fea breezes *. 



The caufe of this may be that near the fea th« temperature The myrtle 

 is more regular than within land, and fudden changes we pcr^ J j^V "J^JJJ 

 haps unfavourable to evergreens: for we always find thofe the temperature 



with broad leaves grow beft in the made, and thofe with nar-Xf"* ,efs * . 



6 ■ . Other remarks, 



row leaves on elevated places, in both of which fituations the 



temperature is more regular than in open expofures or confined 

 vallies. And we may often obferve plants growing on a fome- 

 what elevated fituation, if fheltered from ftrong winds, lefs 

 hurt in a fevere winter, than others in low warm and fheltered 

 places. For vapour being railed in fuch places during the 

 day, produces a greater degree of cold by condenfation and 

 evaporation in the night, than is experienced in other places 

 where the coldnefs of the air prevented the rife of vapour 

 during the day. From every obfervation it appears, that thofe 

 plants which have the leaft lap in winter, or whofe fap is of a 

 refinous or oily nature, fuffer lead from cold, and that the 

 principal caufe of deftru&ion is the veflels being burft by the 

 freezing of the fap. The hoar-froft, which is always mod 

 abundant in vales, tends in a great degree to promote this ; 

 for being changed into water, part only of this water is eva- 

 porated during the day, the reft remains to be converted into 

 ice by the cold of the enfuing night. This icy covering en- 

 creafes the cold, till the vital principle +, and refi ft ance given 

 by the formation of the bark to the entrance of cold, are over- 

 come, the fap frozen, and at the fame time the veflels burft 

 by the expanfive force of freezing. This gives the reafon 

 why plants in a fituation where the fun does not thine on them 

 to thaw the hoar-froft, fuffer leaft in fevere feafons ; and that 

 plants removed in autumn, unlefs the (hoots are completely 

 hardened, will be more liable to be injured by froft than thofe 

 of the fame fpecies, the defcent or fixation of whofe fap has 

 received no check by tranfplanting. Miller remarks, that 

 thofe plants which were removed in the autumn of 1739, were 



* See Saint Pierre's Studies of Nature, tranfiated by Hunter, 

 Vol. I. page 607. Dublin edition. 



f See Smith's Trails relating to Natural Hiftory, page 177, and 

 Philofophical Tranfa&ions for 1788. 



moftly 



