i857.] VARIABILITY. 455 



serve. I find in the animal kingdom that the proposition 

 that any part or organ developed normally (/. e., not a mon- 1 



strosity) in a species in any high or unusual degree, comparecj^ '^s''*^ 

 with the same part or organ in allied species, tends to b^e 

 highly variable. I cannot doubt this from my mass of col- 

 lected facts. To give an instance, the Cross-bill is very ab- 

 normal in the structure of its bill compared with other allied 

 Fringillidae, and the beak is eminently variable. The Himan- 

 topus, remarkable from the wonderful length of its legs, is 

 very variable in the length of its legs. I could give mafiy 

 most striking and curious illustrations in all classes; so many 

 that I think it cannot be chance. But I have 7t07ie in the 

 vegetable kingdom, owing, as I believe, to my ignorance. If 

 Nepenthes consisted of one or two species in a group with 

 a pitcher developed, then I should have expected it to have 

 been very variable ; but I do not consider Nepenthes a case 

 in point, for when a whole genus or group has an organ, 

 however anomalous, I do not expect it to be variable, — it is 

 only when one or few species differ greatly in some one part 

 or organ from the forms closely allied to it in all other re- 

 spects, that I believe such part or organ 'to be highly variable. 

 Will you turn this in your mind } it is an important apparent 

 law (I) for me. 



Ever yours, 



C. Darwin. 



P. S. — I do not know how far you will care to hear, but 

 I find Moquin-Tandon treats in his ' Teratologic ' on villosity 

 of plants, and seems to attribute more to dryness than alti- 

 tude ; but seems to think that it must be admitted that 

 mountain plants are villose, and that this villosity is only 

 in part explained by De Candolle's remark that the dwarfed 

 condition of mountain plants would condense the hairs, and 

 so give them the appearaitce of being more hairy. He quotes 

 Senebier, ' Physiologic Vegetale,' as authority — I suppose the 

 first authority, for mountain plants being hairy. 



If I could show positively that the endemic species were 



