152 GENETICS AND EUGENICS 



varieties. Red aleurone color is a recessive allelomorph of 

 black. Both are dominant over colorless aleurone. Red 

 seed-coat is a character dominant over colorless seed-coat, 

 and a seed-coat striped with red is allelomorphic to unstriped 

 seed-coat. A highly starchy condition of the endosperm is 

 found in ordinary varieties of field corn, which have rela- 

 tively plump seeds. A recessive allelomorphic condition is 

 found in sweet corn cultivated for table use, in which sugar 

 predominates in the seeds so that on drying it takes on a 

 shriveled, wrinkled appearance. A different recessive varia- 

 tion is found in a variety of corn recently imported from 

 China, in which the endosperm is waxy rather than sweet or 

 starchy. If the variety with waxy endosperm is crossed with 

 sweet corn, starchy corn is obtained by reversion in Fi, and 

 in F 2 all three sorts are obtained in the ratio, nine starchy 

 to three waxy, and four sweet. 



5. Forms of leaves. Leaf form in many cultivated plants 

 is known to vary by Mendelizing units. In the nettle 

 {Urtica) Correns has shown that the much-serrated leaves of 

 one natural variety possess a character dominant over the 

 nearly entire leaves of another variety (Fig. 115). In Cheli- 

 donium majus, a laciniate leaf form is known to be recessive 

 to the normal form of leaf. In Primula sinensis, normal pal- 

 mate leaves are dominant over fern-like pinnatifid leaves. In 

 a great number of plants hairy or spinous leaves, stems, or 

 fruits, are known to be dominant (more or less completely) 

 over smooth ones. 



6. Form of stem. One of the seven discontinuous varia- 

 tions with which Mendel dealt in his original paper is in- 

 volved in the difference between tall and dwarf races of peas 

 and beans. The original and the dominant form of stem is 

 the tall form. Dwarf form, in which the internodes of the 

 plant are relatively short, segregates in regular recessive 

 fashion. Semi-dwarf races also exist, which indicate either 

 imperfect segregation or alternative forms of dwarfness. 

 Dwarfness occurs as a variation alternative to normal tall 

 form in snapdragons, nasturtiums, and many other culti- 

 vated plants. 



