20 



THE AMERICAN NATURALIST [Vol. XLIX 



logical goal is very clear. A great deal of the pessimism 

 which at the present time is sending too many biologists 

 after strange gods in other scientific shrines is doubtless 

 to be traced to the failure to make this distinction. It may 

 not be possible to make the distinction in all cases even 

 among the higher plants ; but it certainly will be necessary 

 to realize its significance. Probably plants will in regard 

 to this possibility enjoy in this respect, as in so many 

 others, an advantage over animals in the studies of the 

 experimental evolutionist. 



We may now consider with advantage the status of the 

 species of the genus (Enothera. The pollen sterility 

 which characterized them all to a greater or less degree 

 is indisputable evidence of their probable hybrid origin. 

 The general situation in regard to the criteria of hybrid- 

 ism in plants has been recognized for nearly a hundred 

 years. It has been made clear by Bateson in regard to 

 (Enothera lemarckiana. The observations chronicled 

 here appear to make it obvious that all the species of 

 (Enothera are in the same boat genetically, that is that 

 they are all of hybrid origin. They likewise probably will 

 all be found to 11 mutate" just as 0. lamarcJciana, 0. bien- 

 nis, etc., are already known to do. It may appear later 

 that there are certain species which have escaped, through 

 geographical isolation or other causes, the mingling of 

 blood, which is certainly characteristic of the (Enotheras 

 of the Eastern United States. So far as we know them 

 at present, the species of (Enothera are obviously in the 

 same position as such species as Rosa blanda, that is they 

 are crypthybrids. Doubtless the peculiarities of 0. la- 

 marckiana, 0. biennis, etc., can be more clearly explained 

 in the present condition of our knowledge as the result of 

 hybrid origin than in any other way. It follows that the 

 doctrine of mutation so far as it depends for its support 

 upon the (Enotheras is in a discredited condition, as an 

 explanation, in any proper sense of the term, of the 

 origin of species. 



