126 Plant Genetics 



a limitation expressed by the statement that at the 

 reduction division allelomorphs never go to the same 

 nucleus, that is, the reduction division would never 

 produce a spore whose nucleus would contain both A 

 and a, for A and a are allelomorphs. All of this is 

 evident in connection with the Mendelian diagrams. 

 It should be remembered, however, that when it is said 

 that a spore or a gamete contains only half as many 

 chromosomes as does a sporophyte the whole truth has 

 not been stated. In fact, such a statement does not 

 include the most significant fact from the Mendelian 

 point of view; that is, that a spore 

 or a gamete never contains both of a 

 pair of allelomorphs in the nucleus. 

 It should be realized that 4 and 8 

 chromosomes are used only as con- 

 venient representative numbers, for 

 in plants there is a wide variation as 

 to these numbers, and in the vast 

 majority of cases the sporophyte number is consider- 

 ably more than 8. In angiosperms, for example, the 

 haploid number ranges from 3 in Crepis to 45 in 

 Chrysanthemum. The statement that the essential 

 feature of the reduction division is to separate allelo- 

 morphs into different nuclei is simply a statement of 

 the theory of segregation, which is the fundamental 

 feature of Mendel's law. If this statement is not 

 true Mendel's law is not true, and all of our ideas of 

 inheritance will have to be reconstructed. 



With this in mind, it may be considered how a knowl- 

 edge of inheritance in gametophytes may be of service. 

 For convenience we will consider first a single pair of 



