244 REPRODUCTION 



and its resulting seeds, as many as possible, are planted by 

 themselves, and if the offspring show the same combination 

 the homozygote condition is demonstrated, but if they split 

 into new combinations we know that for some characters 

 they were heterozygote. By selecting for seed production 

 only those offspring that show the original combination, and 

 planting the seeds of each of these separately, the homozygote 

 condition will be found sooner of later, and by self-pollination 

 it may be multiplied indefinitely true to its character. Infer- 

 tility with self-pollen, and serious loss of vigor resulting from 

 self-fertilization are sometimes disturbing factors. 



Exceptions to the Rules. — That we might keep to the main 

 path in our discussion, we have left to the end mention of excep- 

 tions to the rules that have been formulated for us by Mendel 

 and other experimenters in hybridization. Dominance of one 

 contrasting character over another does not always occur. On 

 the contrary the two characters sometimes blend, or express 

 themselves independently side by side, as when a cross between 

 white and red flowers gives pink flowers, or striped red and 

 white. 



It seems, too, that segregation does not always take place during 

 spore-formation of the F^ and succeeding generations, that is, 

 sometimes propagation by seed can straightway take place true 

 to the type that appears in the Fj generation, but this is of much 

 rarer occurrence than is failure in dominance. 



Sometimes, again, entirely new or apparently new qualities 

 made their appearance in hybrids, as when a cross between two 

 smooth varieties gives hairy offspring (Matthiola or ten-week 

 stocks), or when red flowers crossed with yellow gives white 

 (sweet peas and stocks), or when a cross between two white 

 flowered varieties gives red flowers (sweet peas), or when red 

 flowers crossed with white flowers gives yellow (Mirabilis jalapa) . 



These surprising results are not necessarily outside the domain 

 of Mendelian principles. An analysis of the causes of different 

 colors in flowers will sometimes lead to a clear explanation of 

 anomalous results. Let us examine the case of the white- 



