LECT. in VARIATION IN PHYSIOLOGY 115 



and if I dwell somewhat upon the topic, it is owing to 

 the fact that this sort of difference has not been as much 

 investigated as it ought to have been. Between two 

 species, however closely allied, between two varieties or 

 races of the same species, there are not only those slight 

 external differences upon which so much stress is laid 

 by morphologists ; there are internal, chemical and 

 physiological differences which are most likely of 

 greater importance. For instance, Naudin cultivates in 

 his gardens at Collioure, in the south of France, a 

 number of plants of a species of Echium ; part are 

 indigenous, part come from the Canary Islands ; they 

 all exactly resemble each other, no external difference 

 is perceptible ; they differ in origin only. During the 

 night, the frost comes ; all the Canary plants die, 

 while the plants of France resist. There is some 

 difference in their constitution or physiology, some 

 difference due to habit, to adaptation, however it 

 may be called, and the result is that life may continue 

 under circumstances which cause it to cease when this 

 difference does not exist. This is one fact among 

 a thousand, and horticulturists and breeders could 

 provide many similar examples. It shows that, 

 even in cases where no external differences are 

 perceptible, variations do exist in given circum- 

 stances which may be of the highest importance, and 

 decide life or death. Though they are not always of 



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