CARE REQUIRED IN SELECTION. 155 
of animals and plants. To practised gardeners and farmers, 
you may give distinct commissions, and say, for example, 
I wish to have this species of plant with this or that colour, 
and with this or that shape. Where breeding has reached 
the perfection which it has attained in England, gardeners, 
and farmers are frequently able to furnish to order the 
desired result within a definite period, that is, at the end of 
a number of generations. Sir John Sebright, one of the most 
experienced English pigeon-breeders, could assert that in 
three years he would produce any form of feather, but that 
he required six years to obtain any desired form of the head 
and beak. In the process of breeding the merino-sheep of 
Saxony, the animals are three times placed on a table beside 
one another, and most carefully compared and studied. 
Each time only the best sheep with the finest wool are 
selected, so that in the end, out of a great multitude, there 
remain only some few animals, but their wool is exquisitely 
fine, and only these last are used in breeding. We see, 
therefore, that the causes through which, in artificial 
breeding, great effects are produced, are unusually simple, 
and these great effects are obtained simply by accumulating 
the differences which in themselves are very insignificant, 
and become surprisingly increased by a continually repeated 
selection. 
Before we pass on to a comparison of this artificial with. 
natural breeding, let us see what natural qualities of the 
organisms are made use of by the artificial breeder or 
cultivator. We can trace all the different qualities which 
here come into play to physiological fundamental qualities of 
the organism, which are common to all animals and plants, 
and are most closely connected with the functions of 
