External and Internal Factors in Evolution ars 
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 
