122 



THE THEORY OF THE GENE 



The 24 chromosomes of the tetraploid at the second 

 maturation division are showTi in Fig. 74. They re- 

 semble those of the diploid at the same stage. Half of 

 each passes to one pole, half to the opposite pole. Belling 

 records that in 68 per cent the distribution is regular, i.e., 

 24 to each pole (24-|-24). In 30 per cent of cases the dis- 



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M 



^ 







^ ^ 



Fig. 76. 

 Conjugation of the chromosomes of the tetraploid of Datura stra- 

 monium. Four like chromosomes unite to malce up each group. 

 (After Belling and Blakeslee.) 



tribution gives 23 at one pole and 25 at the other (23+ 

 25). In 2 per cent there were 22 at one pole and 26 at the 

 other. In one case the distribution was 21-27. The result 

 shows that irregularities of distribution are not uncom- 

 mon in the tetraploid Datura. A further test of this was 

 made by self-fertilizing a tetraploid. The progeny was 

 grown to maturity and the chromosomes in their germ- 

 cells counted. The number of chromosomes in 55 of the 

 plants was 48 ; in five plants it was 49 ; in one plant it was 

 47 ; in another it was 48 ( I). If the distribution in the egg- 

 cells is like that in the pollen cells, it follows that the 



