478 Mutations 



only vicinists, caused by stray pollen grains 

 from another culture, cannot of course be de- 

 cided with sufficient certitude. 



Here I might refer to the observations con- 

 cerning the invisible dimorj)hous state of the 

 flowers of the normal toad-flax. Individuals of 

 the same type, when fertilized with each other, 

 are nearly, but not absolutely, sterile. The 

 yield of seeds of my peloric plants agrees fairly 

 well with the harvest which I have obtained 

 from some of the nearly sterile pairs of indi- 

 viduals in my former trial. Hence the sugges- 

 tion is forced upon us that perhaps, owing to 

 some unknown cause, all the peloric individuals 

 of my experiment belonged to one and the same 

 type, and were sterile for this reason only. If 

 this is true, then it is to be presumed that all 

 previous investigators have met the same con- 

 dition, each having at hand only one of the two 

 required types. And this discussion has 

 the further advantage of showing the way, 

 in which perhaps a full and constant race of 

 peloric toad-flaxes may be obtained. Two indi- 

 viduals of different type are required to start 

 from. They seem as yet never to have arisen 

 from one group of mutations. But if it were 

 possible to combine the products of two muta- 

 tions obtained in different countries and under 

 different conditions, there would be a chance 



