118 THE AMERICAN NATURALIST [Vol. LV 



A very common abnormality consists of small yellow 

 spots thickly distributed on all the leaves which develop 

 later than the seedling stage. While undoubtedly inter- 

 fering with the proper functioning of the chlorophyl, the 

 effect of this abnormality is not serious. Even in breed- 

 ing experiments seed may be saved from a spotted plant 

 and in a population containing these partly chlorotic in- 

 dividuals many of the ovules on the most vigorous plants 

 will be fertilized by pollen from affected plants. It is 

 easy to see how characters of this kind persist. 



A more serious and less common abnormality is one 

 that prevents the leaves from unrolling properly, with the 

 result that the plant is bent and contorted and in extreme 

 cases never reaches maturity. Seed would seldom be 

 saved from plants affected with this disorder, but they 

 frequently produce pollen in normal quantities and the 

 character in consequence is widespread and difficult to 

 eliminate. 



Albino seedlings may be taken as an example of a still 

 more serious type of abnormality. In this case all indi- 

 viduals that show the character die in the seedling stage. 

 It might appear at first that disorders of this type would 

 be self-eliminating. The character is recessive, however, 

 and in many strains there are plants which are hybrid 

 for the albino character. These hybrid plants show no 

 trace of the character, yet one half of the pollen grains 

 and one half of the ovules carry albinism. If either of 

 these unite with one of their kind an albino plant results, 

 while if they unite with a normal gamete another hybrid 

 plant like the parent is produced. Such characters may 

 be carried along in this manner for any number of gen- 

 erations in a completely latent form, coming into expres- 

 sion only when pollen grains and ovules both bearing the 

 character chance to unite. 



Breeding experiments have shown that the more con- 

 spicuous of these abnormalities are recessive Mendelian 

 characters which have come into expression through the 

 chance meeting of male and female gametes both bearing 



