THE BEGINNINGS OF LIFE. 597 



characters thus suddenly acquired, that a nectarine pro- 

 duced by bud-variation has propagated itself by seed/ 



Changes of this kind and several others which Mr. 

 Darwin records l are doubtless due to some molecular 

 modification, brought about in an unknown manner, in 

 the tissues of the bud which varies; so that the pro- 

 duction of the nectarine structure is the result of the 

 altered balance and the new moving equilibrium which 

 becomes necessitated in the tissues of the growing part. 

 Such an explanation of these apparently c spontaneous J 

 changes in plants may be illustrated by alterations 

 which are liable to occur in certain parts of animals 

 when they are exposed to particular influences. Thus 

 Mr. Wallace says 2 : c The Indians (of South America) 

 have a curious art by which they change the colours of 

 the feathers of many birds. They pluck out those from 

 the part which they wish to paint, and inoculate the 

 fresh wound with the milky secretion from the skin of 

 a small toad. The feathers grow of a brilliant yellow 

 colour, and on being plucked out, it is said, grow 

 again of the same colour without any fresh operation.' 

 Although this change seems to be producible at will by 

 a definite agent, we really know no more concerning 

 the actual steps of the process by which it is produced, 

 than we know concerning the intimate nature of the 



1 Somewhat analogous changes, for instance, occasionally occur in 

 rose-trees, whereby a moss-rose suddenly appears upon a tree belonging 

 to a totally different variety (loc. cit, pp. 379-381). 



2 ' Travels on the Amazon and Rio Negro,' p. 294. 



