84 WHEAT PRODUCTION IN NEW ZEALAND 
3. Scheme of Work. 
Since wheat is normally self-fertilized, different races 
can grow together in the same crop and yet preserve 
during an indefinite number of generations their indi- 
vidual characteristics. Chance variations induced by 
accidental crossing or by unknown causes do, however, 
occur, and so a field of ordinary wheat, even though pure 
as to variety, contains a large number of strains, the 
differences between which are easily discernible to the 
practised eye, just as m the show ring judges are able 
to discern different strains in a pure breed of sheep, and 
are able to name the breed of many a sheep merely 
from the appearance of the wool or from the configur- 
ation of the limbs or body. Now, some sheep have the 
characteristic of fattening more quickly than others on 
the same feed, and this is naturally a quality highly 
valued. If a hundred sheep are running in the same 
field and they all have the same feed the fattest are 
congenitally early fattening, and can therefore be bred 
from with confidence that they will transmit this 
character. But if one were given a large flock of sheep 
that had been fed under different but unknown con- 
ditions, then some would be congenitally fat, but others 
only accidentally so, that is fat because they had received 
better or more plentiful feed. These latter, if used for 
breeding, would not produce early fattening lambs. 
What could the breeder do? He could only pick out the 
fattest sheep and breed from them, because he could not 
distinguish the congenitally fat from the accidentally 
fat. He would probably mix all the breeding sheep 
together and note the fatness of the resulting flock, when 
all fed under the same conditions. This would be mass 
selection. The average of the offspring would be fatter 
than the average of the flock from which their parents 
were selected, but there would be fat lambs and lean 
ones, because some would be descended from congenitally 
