no THE THEORY OF THE GENE 



have almost four times the volume of the normal type; 

 those of the stigma three times the volume ; those of the 

 petals twice the volume and the pollen mother cells are 

 about one and a half times larger. The nuclei of the latter 

 have, in gigas, twice the volume of the parent type. The 

 cells in the two types also differ sometimes markedly in 

 their superficial dimensions. Most species of evening 

 primroses have 3-lobed discoidal pollen grains, some of 

 those of gigas are 4-lobed. 





a 



Fig. 65. 



a, The fourteen diploid chromosomes of Oenothera Lamarckiana; 



T), the twenty-eight diploid chromosomes of O. gigas. 



The maturation of the pollen mother cells has been 

 studied by Gates, Davis, Cleland, and Boedijn. Gates 

 reports that in 0. Lamarckiana there are, as a rule, 14 

 pairs of bivalent chromosomes (gemini) in the giant. At 

 the first maturation division, half of each bivalent goes to 

 each daughter cell. At the second division each chromo- 

 some splits lengthwise and gives 14 chromosomes to each 

 pollen grain. A similar process presumably occurs in 

 the ripening of the ovules. Davis describes the chromo- 

 somes of 0. Lamarckiana that emerge from the synaptic 

 tangle as stuck together somewhat irregularly and not 

 strictly in side to side union. Later they move toward one 



