114 THE ORIGIN OF SPECIES 



yet been found anywhere except in caves; yet those which in- 

 habit the several caves of Europe and America are distinct; but 

 it is 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, excepting in their 

 present secluded abodes. Far from feeling surprise that some of 

 the cave-animals should be very anomalous, as Agassiz has re- 

 marked in regard to the blind 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 ex- 

 posed. 



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 acclimati- 

 zation. 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 during 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 they live is often overrated. We may 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 ani- 

 mals brought from different countries which are here perfectly 

 healthy. We have reason to believe that species in a state of nat- 

 ure 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 

 becoming, to a certain extent, naturally habituated to different 

 temperatures; that is, they become acclimatized; thus the pines 

 and rhododendrons, raised from seed collected by Dr. Hooker 

 from the same species growing at different heights on the Hima- 

 layas, were found to possess in this country different constitutional 

 powers of resisting cold. Mr. Thwaites informs me that he has 

 observed similar facts in Ceylon; analogous observations have 



