Naturalization of Plants. 215 



if this can, within certain limits, be diminished by habit, as in 

 animals, naturalization within these limits, is not impossible. 



If this be plausible, the road is obvious, for vegetables as for 

 animals ; it is gradation of climate and a succession of generations. 

 Thus it has been widely effected for animals, and thus it may 

 perhaps be effected for vegetables ; if less widely, from the want 

 of powers productive of heat to resist the excess of a new and 

 destructive influence. Let us not decide on this impossibility d 

 priori; not, philosophically, till we are better acquainted with 

 vegetable physiology, and, in no case, till we have conducted a 

 much wider series of experiments than the few coritrovertible 

 ones already made. 



There is a plausibility respecting this view of the sensibilities of 

 plants. The Nasturtium, in the full vigour of flower and fruit, 

 is killed in an instant by frost, vigorous to the very moment of 

 freezing. Our own herbaceous plants, of structures as similar 

 as the eye can ascertain, go on resisting, many of them, through- 

 out a severe winter. The difference is not in the vessels, in the 

 circulating system, in the fluids. In both they would equally be 

 frozen ; but, to one, this condition is death, while the other heeds 

 it not. "Where then is the difference, if there be not a nervous 

 system ? that system the seat of life, the system whose action is 

 destroyed by poisons, destroyed even by the narcotic poisons. 

 Plants are poisoned as animals are ; not by an action on their 

 fluids, not under a system of humoral pathology (to use old medical 

 language), since their primary circulating fluid is water, not to be 

 decomposed by the poisons which kill them ; as the blood of 

 animals might be, and has been, supposed to suffer. But I must 

 reserve this subject for another occasion. It is sufficient to have 

 thrown it out as a hint on this particular question ; and should it 

 prove a fact, as it cannot fail to prove, should the various sensi- 

 bilities of plants prove analogous to those of animals, we shall be 

 enabled to explain many more phenomena than the tenderness of 

 the Caper, the affections of plants for peculiar situations, climates, 

 elevations, what not, phenomena which have long been a stumbling- 

 block in the way of botanical philosophy, 



