Parthenogenesis and Vegetative Apogamy 121 



of this indicates that the origin of embryos cannot always 

 be assured, and apogamy is a factor that may at any 

 time upset any expectation based on Mendel's law 

 without violating that law. If Mendel's law is based 

 on the act of fertiUzation, and that act does not occur, 

 the result has nothing to do with the law. 



In view of what has been said, the recent movement 

 of some plant geneticists to include the lower plants in 

 their work will be understood. This results in the 

 following opportunities. In the study of sexual repro- 

 duction the simpler plants (such as algae) have sexual 

 structures that are not involved with other structures, 

 and the whole performance of fertilization and embryo 

 development is in sight and capable of control. The 

 difference between a sex act and embryo development 

 under cover and in the open, when observation and 

 control are desired, is obvious. Furthermore, back of 

 inheritance through the sex act is inheritance through 

 spores. Such inheritance needs investigation in con- 

 nection with inheritance through sex. There are cer- 

 tain things that all forms of inheritance have in 

 common, and these things should be kept distinct from 

 those which are pecuUar to sex inheritance. Only in 

 this way can any knowledge be reached of the special 

 role of sex in inheritance and the peculiar features it 

 has added. 



A practical plant breeder may be interested only in 

 the fact that he can obtain a new individual from a seed 

 the pedigree of whose embryo in the nature of things 

 cannot be demonstrated; but a scientific plant breeder, 

 that is, a geneticist, must be interested in the conditions 

 that determine inheritance, and these will be discovered 



