THE STUDY OF NATURAL SELECTION 129 



be quite out of the question to do more than determine whether the 

 death rate is selective or random, and in such cases these first steps 

 may be of very high importance indeed. Again, it may be feasible to 

 plunge at once into the second problem by testing the value of 

 character after character in the battle for life. In this ease both 

 phases are simultaneously taken up. These points will be made clear 

 by illustrations. 



II. Further Attempts to Ascertain whether the Death Kate 

 is Selective and to Determine the Intensity of Selection 

 The first problem to be taken up is therefore that of the existence 

 or non-existence of selective mortality. In a considerable range of 

 living forms it is desirable to know whether natural selection is opera- 

 tive, even though it is for the time being out of the question to say 

 how it is operative, i. e., what particular characteristics make for in- 

 capacity or for fitness. 



A. The Simple Demonstration of the Existence of a Selective Mortality 

 Studies on Plants. — A first illustration of the importance of the 

 simple determination of the selective or non-selective nature of the 

 death rate is to be seen in the cases of the northward extension of 

 cereals or other cultivated plants. At present, very little is definitely 

 known concerning the factors actually involved. It has been fre- 

 quently assumed that natural selection through the agency of cold or 

 of the shortness of the growing season has been one of these. Thife 

 view seems to be supported by Waldron's 2 work on alfalfa. He shows 

 that some strains are more resistant to cold than others, and that in 

 the north the less resistant are eliminated. This is all that is neces- 

 sary to bring about adaptation — which already exists in some strains. 

 Another most interesting piece of work differing widely in material 

 and detail, but depending upon the same kind of reasoning, is that of 

 Montgomery. 3 Our common cereals have been cultivated for hundreds 

 or thousands of years with practically no attention to selection or 

 grading until recent times. He suggests that under the system of 

 planting two or three times as many seeds as can possibly come to 

 maturity, a slow development has taken place through a continuous 

 natural selection with the survival of the strongest. 



He has several interesting results for competition, but his most 

 conclusive experiments for selection are those with maize. 4 Planting 



S L. E. Waldron, "Hardiness in Successive Alfalfa Generations/' Amer. 

 Nat., 46: 463-469, 1912. 



*E. G. Montgomery, "Competition in Cereals," Bull. Neb. Agr. Exp. Sta., 

 127, 1912. 



4 E. G. Montgomery, loc. (At. Also ' ' Thick and Thin Planting for Growing 

 Seed Corn," Bull. Neb. Agr. Exp. Sta., 112: 28-30, 1909. 



