358 



Bulletin 313 



THE EFFECT OF SELF-FERTILIZATION ON VIGOR 



In timothy, as in other crops, it is necessary to inbreed or self-fertilize 

 different individuals that are chosen as representatives of good types, 

 in order to test the heritability of the characters for which a plant is selected 

 and to secure seed true to the type for propagation. In almost all plants 

 that are normally cross-fertilized, self-fertilization ordinarily results in 

 considerable loss of vigor; and it is important to know what result, if any, 

 timothy gives under such treatment, as a guide to one's judgment of the 

 yield of progenies that have been so treated. In a number of cases in our 

 experiments, self-fertilized seed has been grown immediately beside open- 

 fertilized seed of the same individual. The open-fertilized seed used in 

 such cases would thus have been cross-fertilized in the degree usually 

 present in seed produced under ordinary field conditions. These yields 

 compared with one another give a clear indication of the effect of inbreed- 

 ing. In the following table are given the results of nine such tests with 

 different types, each test including the average yields of about twenty- 

 four plants for the second and third crop years : 



TABLE 2. Showing Comparative Effect in Timothy of Open-fertilization 

 AND Self-fertilization on the Average Yield per Plant of Progeny 



In the above table the average yield of the original plant for three 

 seasons is given in the second column. In the third column is given the 

 average yield per plant for two seasons when each type is propagated in 

 clonal rows. Each of these cases includes the average yield of 16 plants 

 for the second and third crop seasons. In the fourth column is given the 



