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 inoperative; when a higher mortality is demonstrated, selection is tending to weed it out; when a lower mortality exists, natural selection is allowing 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. Montgomery[1] in addition to his studies on competition in cereals, has investigated the survival of plants from small or undeveloped as compared with that of large plump seeds of wheat and oats when planted in competition.[2] 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[3] the only comparable studies have been made on garden beans.
- ↑ E. G. Montgomery, "Competition in Cereals," Bull. Neb. Agr. Exp. Sta., 127, 1912.
- ↑ 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 different varieties. Inter-varietal competition probably introduces some factors not present when all the individuals are of the same strain.
- ↑ 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
