THE FRAGRANT CALLA 29 



nations of observed phenomena unless all expla- 

 nations of a more tangible character have been 

 proved untenable. And it has seemed to me from 

 the outset that in the case of the evening prim- 

 rose a very much more plausible explanation is at 

 hand than the one devised by the originator of 

 the mutation theory. 



In my own opinion, sports or "mutations" are 

 to be explained as a cumulative effect where 

 tension in a certain direction finally results in a 

 more or less rapid change in one or more individ- 

 uals and may be compared to the breaking of a 

 string by centrifugal force when a weight is more 

 and more rapidly whirled in a circle until the 

 tension is too strong and the weight takes a new 

 course. I am also thoroughly convinced that 

 these more or less numerous abrupt changes are 

 a condition, not a "period" in plant life. 



In a word, the varied tribes of evening primrose 

 which Professor de Vries developed in his gar- 

 dens at Amsterdam were overwhelmingly sug- 

 gestive of various and sundry new forms of 

 hybrid plants that I myself have developed year 

 after year in my experimental farms at Santa 

 Rosa. 



The Primus blackberry, the Phenomenal berry 

 and the sunberry, are, if you wish to so consider 

 them, instances of pronounced mutation, inas- 



