Some Experiments of I^uther Burbank 



is, fixed forms springing up, generally from un- 

 known causes, forms which are not hybrids, and 

 which remain constant; as, for instance, colored 

 flowers which yield white forms, these yielding 

 white constantly in their progeny. T^hese mutations 

 can he produced at will by any of the various means 

 which disturb the habits of the plant. It comes 

 out when the conditions are ripe. New conditions 

 bring out latent traits. I should expect mutations 

 to arise in the American primrose and most other 

 plants under wholly new conditions. Extra food 

 or growth force as well as crossing favors variation, 

 as does abrupt change of conditions of any kind. 

 Five or six generations will usually fix a mutation. 

 Sometimes it is fixed at once." 



' ' On the average, perhaps about six generations 

 fairly fix a variation, but this varies greatly, depend- 

 ing upon previously acquired hereditary tenden- 

 cies. Bringing a species into a new environment 

 disturbs its fixity. Rich soil especially gives rise 

 to variations in growth which seem to be new, and 

 by repetition become inherently fixed. Sometimes 



12 



