HEREDITY 115 



these heads of wheat are of the same kind and 

 collected from the same field. They were grown 

 under similar conditions. To a certain extent some 

 of these variations are inheritable as the facts in 

 Fig. 40 indicate. Given the same amount of 

 timothy seed and planted under as nearly identical 

 conditions as it is possible for man to control, 

 the variation in the size of the bundles of timothy 

 indicates that more timothy is grown from seed 

 selected from plants that were large and bore 

 long heads. These facts are of great importance 

 to man in his constant efforts to improve his crops 

 and domestic animals. (Figs. 39-40.) 



At first thought it would seem as if man held 

 the key to unlock one of Nature's secrets. But 

 the limit in the amount of change that can be 

 produced is soon reached and the trotting horse 

 that has established a record may beget offspring 

 that will never equal his record. The next time 

 that the trotting record is broken, it is by a horse 

 with a different heredity than the one that last 

 made the record. 



Every now and then there seems to be a chance 

 combination of qualities in an offspring which en- 

 ables the possessor to excel. Sometimes such an 

 individual is able to hand these same qualities on 

 for a number of generations, thus producing no 

 new varieties. In all of these studies of variation, 



