EVOLUTION AND MUTATION ii 



case the average is often reached after one more genera- 

 tion. 



I observed the origin of the pcloric toadflax and of a 

 double marigold, and produced, almost artificially, the twisted 

 variety of a Dracocephalum. 



In the case of the toadflax, Linaria vulgaris peloria, the 

 change came suddenly, and more or less unsuspcctedly, 

 after a culture of about eight years. The ordinary form 

 produces, from time to time, some few five-spurred, regular 

 or peloric flowers. At once an individual arose which had 

 such flowers only. The next year the mutation was re- 

 peated. The seeds of the mutated individuals reproduced 

 the new variety almost exclusively, and each plant of it had 

 peloric flowers only. No intermediates were observed, 

 neither in the number of the spurs of the flower nor in the 

 number of the peloric flowers on the plants. It was as sud- 

 den a change as any horticultural sport, but its ancestry 

 had been purely fertilized and carefully recorded so as to 

 leave no doubt concerning the real nature of the mutation. 



The double variety of the corn-marigold (Chrysan- 

 themum segetum) arose in my garden in a culture in wliich 

 I was increasing the number of the ray-florets by contin- 

 uous selection. During four years I had succeeded in in- 

 creasing this number to about sixty on each head, starting 

 from the cultivated variety, with an average of twenty-one. 

 All the ray-florets, however, belonged to the outer rows of 

 the heads, as in the original variety. At once a plant arose 

 which produced some few Hgulate florets in the midst of the 

 disc. This indicated the production of a double race. 

 When the seeds of this mutating individual were sown, the 

 next year, they yielded a uniformly double group; and from 

 this time the new variety remained constant. 



The Dracocephalum moldavicum is an annual garden- 

 plant belonging to a genus in which Morren has described 



