196 THE THEORY OF THE GENE 



Two types of Mexican teosinte have been described by 

 Longley, one, mexicana, an annual type with 20 chro- 

 mosomes (n=:10), the other, perennis, a perennial with 

 40 chromosomes (n=20). Both plants have normal reduc- 

 tion divisions. When the diploid teosinte (n=10) is 

 crossed to Indian corn (n=10), the hybrid has 20 chro- 

 mosomes. At maturation, there are 10 bivalents in the 

 hybrid's germ-cells. This would ordinarily be interpreted 

 to mean that 10 chromosomes of teosinte have united with 

 10 of Indian com. 







a 



b C 



Fig. 110. 

 Eedueed chromosome group, a, of perennial teosinte; 6, of hybrid 

 with maize; c, reduction division of last. (After Longley.) 



When the perennial teosinte (n=20) is crossed to In- 

 dian corn (n=10) the hybrid has 30 chromosomes. At the 

 first maturation division of the pollen mother cells there 

 were found some trivalent groups loosely held together, 

 some bivalents, and some single chromosomes in varying 

 numbers, thus as 4 : 6 : 6 ; or as 1 : 9 : 9 ; or as 2 : 10 : 4, etc. ; 

 see Fig. 110b. At the first division the bivalents divide 

 and the partners move to opposite poles; the trivalents 

 divide, two going to one pole, one to the other ; the singles 

 lag and are distributed (without division) irregularly to 

 the two poles (Fig. 110c). A very unequal distribution 

 results. 



Quite recently a case has been described in which a 



