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 in 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 



