EXTERNAL INFLUENCES AS CAUSES OF VARIATION 223 



The experiments of Bonnier upon this general subject are 

 classic. 1 He divided dandelion, helianthus, and many other 

 plants growing in the valley, and planted one half of each indi- 

 vidual plant on the mountain at an elevation of 2300 to 2400 

 meters, leaving the other half in the valley (how much below 

 he does not say). As the division was made by a vertical cut 

 through the fleshy root, the two halves must have been practi- 

 cally alike. 



He found that the portions on the mountain developed plants 

 much smaller than those in the valleys. The difference was 

 mainly in the length of the internodes, not in their number. 

 The leaves of the dandelion were less than one fifth as long 

 when drawn to scale, and the flower stalks were not one tenth as 

 long. The mountain plants in general developed higher colors. 



Darwin tells us that the medicinal qualities of digitalis are 

 " easily affected by culture," and that " the wood of the Amer- 

 ican locust tree (Robinia) when grown in England is nearly 

 worthless, as is that of the oak tree when grown at the Cape of 

 Good Hope." 2 The same author quotes Sir J. E. Tennent as 

 saying that "in the Botanic Gardens of Ceylon the apple tree 

 ' sends out numerous runners underground, which continually 

 rise into small stems, and form a growth around the parent 

 tree.' " 3 If this be true, its naturally slight tendency to sprout 

 has in this locality developed into a pronounced habit. 



Sheep, especially the merinos, are cosmopolitan, and yet they 

 succeed nowhere else as in New Zealand. On the other hand, 

 according to Darwin they seem not to succeed in the West 

 Indies or on the west coast of Africa, where " the wool disap- 

 pears from the whole body except over the loins." 4 The writer 

 has seen the same thing in Brazil, except that the best-clothed 

 portion of the body was the back of the neck, the same spot on 

 which the vicuna bears its fur. 



The statement is frequently made that fat-tailed sheep rapidly 

 lose this character when removed from their native saline pas- 

 tures, but the assertion needs confirmation, for the writer has 



1 C. Bonnier, Recherches experimentales sur 1'adaptation des plantes au climat 

 alpin. Annales des sciences naturelles, 7 e Serie, Tome XX, 1895. 



2 Darwin, Animals and Plants, II, 264. 3 Ibid. p. 266. * Ibid. I, 102. 



