HEREDITY IN PLANTS 



453 



[Chap. XXXVII 



of like chromosomes^ and two pairs of unlike chromosomes, there are 

 only two different ways in which the chromosomes may be oriented, and 

 four different kinds of spores, eggs, or sperms may be formed. If there 

 are two pairs of like chromosomes and only one pair of unlike chromo- 

 somes, there is but one possible orientation and two kinds of spores, 

 sperms, or eggs. If there are 24 pairs of unlike chromosomes, there are 



B 



^^ 



C 



o 



^^. 



•. 



CD 



•. 



Fig. 211. a diagrammatic representation of the behavior of chromosomes during 

 the formation of microspores from microsporocytes, or of megaspores from mega- 

 sporocytes in a plant having three pairs of unhke chromosomes. 



What will be the chromosome complement of the sperms and eggs formed in 

 this plant? 



8,388,608 different ways in which the chromosomes may become ori- 

 ented, and a possible 16,777,216 different kinds of spores, sperms, or 

 eggs. The number of different kinds of microspores or megaspores and 

 consequently of different kinds of sperms or eggs that can be produced 

 by a plant may be represented by 2", where n is the number of pairs of 

 unlike chromosomes in the cells of the spore-bearing plant. 



Chromosomes in cross-fertilization. Let us see if the facts we have 

 learned about hereditary factors and chromosomes in relation to the life 

 history of a plant are sufficient to explain the relative numbers of the 

 different kinds of plants obtained by crossing and selling in snapdragon, 

 as described earlier in this chapter (Fig. 205). One of the eight chromo- 

 somes in the gametes of the red-flowered plant contained at least one 

 gene with the potentiality of conditioning the formation of red pigment 



