External and Internal Factors in Evolution 315 



may be a hundred years old and not be more than three feet 

 high, are in part the result " of mechanical processes which 

 prevent the spreading of the branches, and in part of a starv- 

 ing process which consists in cutting most roots and in keeping 

 the plant in poor soil." 



As an example of the sudden appearance of a new varia- 

 tion the following case is interesting. A variety of begonia 

 is recorded as having appeared quite suddenly at a number of 

 places at the same time. In another case a narcissus which 

 had met with adverse circumstances, and had then been 

 supplied with a chemical manure in some quantity, began to 

 bear double flowers. 



Amongst animals the following cases of the appearance of 

 sudden variations are pointed out by De Varigny. " In Para- 

 guay, during the last century (1770), a bull was born without 

 horns, although his ancestry was well provided with these 

 appendages, and his progeny was also hornless, although at 

 first he was mated with horned cows. If the horned and the 

 hornless were met in fossil state, we would certainly wonder 

 at not finding specimens provided with semi-degenerate horns, 

 and representing the link between both, and if we were told 

 that the hornless variety may have arisen suddenly, we should 

 not believe it and we should be wrong. In South America 

 also, between the sixteenth and eighteenth centuries the niata 

 breed of oxen sprang into life, and this breed of bulldog 

 oxen has thriven and become a new race. So in the San 

 Paulo provinces of Brazil, a new breed of oxen suddenly 

 appeared which was provided with truly enormous horns, the 

 breed of franqueiros, as they are called. The mauchamp 

 breed of sheep owes its origin to a single lamb that was born 

 in 1828 from merino parents, but whose wool, instead of being 

 curly like that of its parents, remained quite smooth. This 

 sudden variation is often met with, and in France has been 

 noticed in different herds." 



The ancon race of sheep originated in 1791 from a ram 



