ARE RECESSIVES LOSSES OF GENES? 



83 



nucleus results (Fig. 47), which by division gives rise to 

 the triploid nuclei of the endosperm cells. In floury corn 

 the endosperm is composed of soft starch, while flint corn 

 has a large amount of corneous starch in the endosperm. 

 If a floury corn be used as the female parent (ovule) and 



polar 

 nucleus 



synergidae 



--ovum 



ego; nucleus 

 sperm nucleus 



ertili'zed 



endosperm 

 nude « 



Fig. 47. 



Three stages in the fertilization of the egg-nucleus in the embryo 

 sac of plants. In b the two maternal haploid nuclei and the single 

 paternal haploid sperm nucleus are shown. By their union the trip- 

 loid endosperm is produced as shown in c. (After Strasburger and 

 Guinard from Wilson.) 



flinty corn as the male parent (pollen) the seeds pro- 

 duced by the F a plant have floury endosperm. The result 

 shows that two floury genes are dominant over one flinty 

 gene (Fig. 48a). If the reciprocal combination is made, 

 flinty female parent and floury pollen, the F x seeds are 

 flinty (Fig. 48b). Here two flinty genes dominate one 

 floury. It is a matter of choice which gene is chosen to 

 represent the absence of the other. If the absence is floury, 

 then two absences would be said to dominate one presence 



