204 INBEEEDING AND OUTBEEEDING 



ably partakes of certain features of both parents. If 

 forced to depend upon food supplied by only one parent it 

 might be handicapped to some extent in comparison with 

 another embryo supplied with food which was intermedi- 

 ate with respect to the two parents. If endosperm hybrid- 

 ization does indeed supply such a need, the fact that the 

 endosperm is also increased in amount would have equal 

 importance. It may well be that to fill either purpose 

 endosperm hybridization has sufficient value to account 

 for its maintenance in the angiosperms. However this 

 may be, increased adaptability through recombination of 

 characters which is such an important factor in sexual 

 reproduction has no significance in this case, as the endo- 

 sperm does not perpetuate itself. 



Additional light may be thrown on the importance of 

 heterosis in sex origin from the part it possibly has had in 

 a related series of events. In the algae and mosses, the 

 principal life processes are carried on in the haploid gen- 

 eration and the parts which result from fertilization and 

 produce the spores are relatively insignificant and are 

 dependent upon the gametophyte for maintenance. How 

 the sporophyte has gradually become more specialized, 

 taking up the manufacture of food for itself until finally 

 the relations are changed completely, are matters of 

 common knowledge. This series of events is usually 

 referred to as the rise of the sporophyte and decline of 

 the gametophyte. 



Just why there has been this radical and complete 

 change in the plant kingdom is rather difficult to explain, 

 but it should be noted that the increased variability and 

 greater adaptability which seems reasonable in account- 

 ing in a large measure for the survival of sex, is not 



