134 THE POPULAR SCIENCE MONTHLY 



Groth and Martin, but they justly emphasize the great difficulty of the task and 

 the need of wider and better statistics. 



B. The Selective "Value of Particular Characters 



Whenever possible students of natural selection have plunged at 

 once into the problem of the way in which elimination takes place. 

 When only the normal mortality is found for individuals with a given 

 character, or intensely of the given character, selection is there inoper- 

 ative; when a higher mortality is demonstrated, selection is tending to 

 weed it out; when a lower mortality exists, natural selection is allow- 

 ing it to gain ground in the struggle for existence. In the following 

 paragraphs the results secured in this field are set forth. 



Seed Weight and Mortality. — Among flowering plants, the highest 

 death rate occurs in the seedling stage, just as among animals the force 

 of natural selection is well nigh spent by the time a given generation 

 reaches maturity. 



It seems most important, therefore, to inquire what influence, if 

 any, the characteristics of the seed or of the plant from which it was 

 harvested have upon its viability. Closely correlated with, but quite 

 distinct from, this problem is that of ascertaining what weight the 

 morphological or physiological characteristics of the young seedling 

 has in determining its chances of survival. It is only recently that 

 these promising fields have been entered. 



Consider first the visible characteristics of the seed itself. Mont- 

 gomery 20 in addition to his studies on competition in cereals, has in- 

 vestigated the survival of plants from small or undeveloped as com- 

 pared with that of large plump seeds of wheat and oats when planted 

 in competition. 21 He finds that when each kind is planted alone a 

 slightly higher percentage of plants is harvested from the large, well- 

 developed seeds. Thus there is a considerable difference in the original 

 quality of the seed. When planted in (inter-varietal) competition 

 there is apparently a still further advantage in the large seeds. But it 

 appears to be very slight indeed. 



It seems that there are almost as many weaklings susceptible to the effect 

 of competition among the plants from large seed as among those from small seed. 



As far as I am aware 22 the only comparable studies have been made 

 on garden beans. 23 



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

 127, 1912. 



21 Unfortunately, an intra-varietal competition test for seeds of the two 

 kinds could not be made. The large and small seeds were alternated in the row. 

 To distinguish the two at harvest time it was necessary for them to be of dif- 

 ferent varieties. Inter-varietal competition probably introduces some factors not 

 present when all the individuals are of the same strain. 



33 The literature of seed testing is very large and much attention has been 

 given to the produce of large and small seeds. Practically all the work has been 



