580 Mutations 



of the highest importance and admits of only 

 two explanations. One is that intermediates 

 may be assumed to have preceded the existent 

 developed form, and to have died out after- 

 wards. But why should they have done so, 

 especially in cases of recent changes? On the 

 other hand the intermediates may be lacking 

 because they have never existed, the change 

 having taken place by a sudden leap, such as the 

 mutations described in our former lectures. It 

 is manifest that the assumption of hypothetical 

 intermediates could only gain some probability 

 if they had been found in some instance. Since 

 they do not occur, the hypothesis seems wholly 

 unsupported. 



The second point is the constancy of the new 

 type. Seeds should be saved and sown. If the 

 plant fertilizes itself without the aid of insects, 

 as do some evening-primroses, the seed saved 

 from the native locality may prove wholly pure, 

 and if it does give rise to a uniform progeny the 

 constancy of the race may be assumed to be 

 proved, provided that repeated trials do not 

 bring to light any exceptions. If the offspring 

 shows more than one type, cross-fertilization is 

 always to be looked to as the most probable 

 cause, and should be excluded, in order to sow 

 pure seeds. Garden-experiments of this kind, 

 and repeated trials, should always be combined 



