248 REPRODUCTION 



corn is richly heterozygous as ordinarily grown, various strains 

 might be derived by self-fertilization and continued selection 

 that are approximately homozygous, now with one combination 

 of characters, and now with another; and that by crossing all 

 possible pairs of these strains the best combination of parents 

 could be determined for each particular purpose for which corn 

 is used, and for the different environments in which it is grown. 



Sexuality seems to have possible significance in another very 

 important way, namely, in the evolution of organisms — in the 

 derivation of new varieties and species from others preexisting. 

 The possibility of thus obtaining new species has been much 

 in dispute. Theoretically it might be confidently expected, for 

 a new combination of unit characters in hybrids might stimulate 

 the expression of entirely new qualities, or bring secretions 

 into new chemical combinations that might cause alterations in 

 various characters. If now such a hybrid should prove to be 

 stable, a new species would have resulted without the aid of 

 artificial self-pollination and continued selection, to bring it to 

 the constant homozygous condition. When we turn to the 

 records, which is much more to the point, we find Focke's list of 

 more than forty wild species that have been proven of hybrid origin 

 by their duplication through artificial hybridization; we find de 

 Vries's hybrid primrose produced by crossing Oenothera muricata 

 and O. biennis, and Burbank's primus and phenomenal berries, 

 both produced by intercrossing a blackberry and raspberry. 



This suggests to us that in one thing, at least, there is no dis- 

 pute, namely, that the fact of sexuality is of tremendous impor- 

 tance to the work of the plant breeder, for the primary reason 

 that its attendant segregations and recombinations of characters 

 make it possible for him to combine in an improved strain the 

 good qualities of related varieties, while at the same time 

 eliminating those that are undesirable. 



^fc> 



Illustrative Studies 



I. Cut small pieces bearing only a few sporangia from sporo- 

 phylls of Aneimia, Osmunda, or Botrychium, taking care to 



