ACCLIMATIZATION. I33 



possible that the progenitors of these several species, while 

 they were furnished with eyes, may formerly have ranged 

 over both continents, and then have become extinct, ex- 

 cepting in their present secluded abodes. Far from feeling 

 surprise that some of the cave-animals should be very 

 anomalous, as Agassiz has remarked in regard to the bliird 

 fish, the Amblyopsis, and as is the case with the blind 

 Proteus, with reference to the reptiles of Europe, I am only 

 surprised that more wrecks of ancient life have not been 

 preserved, owing to the less severe competition to which 

 the scanty inhabitants of these dark abodes will have been 

 exposed. 



ACCLIMATIZATION". 



Habit is hereditary with plants, as in the period of 

 flowering, in the time of sleep, in the amount of rain 

 requisite for seeds to germinate, etc., and this leads me to 

 say a few words on acclimatization. As it is extremely 

 common for distinct species belonging to the same genus 

 to inhabit hot and cold countries, if it be true that all the 

 species of the same genus are descended from a single 

 parent-form, acclimatization must be readily effected dur- 

 ing a long course of descent. It is notorious that each 

 species is adapted to the climate of its own home: species 

 from an arctic or even from a temperate region cannot 

 endure a tropical climate, or conversely. So again, many 

 succulent plants cannot endure a damp climate. But the 

 degree of adaptation of species to the climates under which 

 thev live is often overrated. We mav infer this from our 

 frequent inability to predict whether or not an imported 

 plant will endure our climate, and from the number of 

 plants and animals brought from different countries which 

 are here perfectly healthy. We have reason to believe 

 that species in a state of nature are closely limited in their 

 ranges by the competition of other organic beings quite as 

 much as, or more than, by adaptation to particular climates. 

 But whether or not this adaptation is in most cases very 

 close, we have evidence with some few plants, of their be- 

 coming, to a certain extent, naturally habituated to differ- 

 ent temperatures; that is, they become acclimatized: thus 

 the pines and rhododendrons, raised from seed collected 



