156 PHYSICAL BASIS OF HEEEDITY 



sometimes one, sometimes another chromosome, there may 

 be genetically several types, but as yet evidence on this 

 point is lacking. 



Irregularities in the germ-cells of (Enothera have been 

 observed by Gates of such a kind that one cell gets 6, the 



<^c$^r 





'^^\> ^z^^ 



d 



m 



Fig. 62. — Somatic chromosomes groups of (Enothera scijitillans, showing variable numbers 

 of chromosomes. (After Hance.) 



other 8 chromosomes. A pollen grain with 8 chromo- 

 somes fertilizing an egg with 7 would give a 15-chromo- 

 some type. When such a 15-chromosome plant forms its 

 egg-cells the supernumerary chromosome having no mate 

 may go to either pole of the spindle, hence eggs of two 



