258 The Pedigree Fainilies. 



ther than observe the mutated individual itself. A num- 

 ber of other combinations are, I suppose, lost in my ex- 

 periments because they cannot be detected until the plants 

 are fairly old, by which time the great majority have been 

 weeded out to make more room.^ Such considerations 

 seem to me to explain how it was that I was able to cul- 

 tivate only so small a number of new species through 

 more than one generation. And it is of course open to 

 question how many of those that I did cultivate could 

 survive the struggle for existence. 



I conclude therefore : Mutability is indiscriminate. 

 Some mutations bear no offspring and disappear forth- 

 with. Between the others and the species already estab- 

 lished natural selection must decide, unless artificial se- 

 lection steps in. 



VII. MufabUity appears periodically. I am led to 

 this conclusion by my experiments ; but I express it at 

 present only tentatively. The fact that of all the species 

 that I have examined so far, only one has proved to be 

 in a state of mutation appears to me sufficient evidence 

 for this conclusion. But further investigations are neces- 

 sary for the establishment of the generalization : and 

 such I have only recently started. I am not of course 

 now in a position to give experimental proof of the 

 existence of mutable and immutable periods : but I have 

 enunciated the hypothesis of their existence as the sim- 

 plest explanation of the remarkable fact that I have so 

 far observed mutations only in a single species ; though 

 plentifully enough in it. 



The above generalizations refer in the first instance 

 to the case which we have observed, namely the muta- 



* For example O. brevistylis and O. leptocart<a are not recogni- 

 zable until just before they flower. 



