246 EVOLUTION, GENETICS, AND EUGENICS 



Dominant Recessive 



Stocks Coloured White 



Wheat and barley Beardless Bearded 



Later ripening Rivett Early ripening Polish 



wheat wheat 



Non-immune to "rust" Immune to "rust" 



Maize "Starch" seed "Sugar" seed 



Nettles (Urtica pilulifera and 



U. dodartii) Serrate leaf margin Entire leaf margin 



Mi nihil is jalapa and M. rosea . Rose colour Other colours 



Mice Coloured coat Albino coat 



Normal "Waltzing" variety 



Rabbits Coloured coat Albino coat 



Angora fur Short fur 



Poultry "Rose" comb of Ham- High serrated "single" 



burghs and Wyandottes comb of Leghorns and 



Andalusians 



Cattle Hornlessness Horns 



Snails Bandless shell Banded shell 



Other instances in plants.— As is well known, there are two almost 

 equally common forms of wild primrose: (A) thrum- types, with 

 short styles and with anthers at the top of the corolla- tube; and (B) 

 pin-types, with long styles and with anthers half way down the tube. 

 The thrum-type is dominant over the pin-type. 



The original species of Chinese primrose {Primula sinensis) has a 

 palmate leaf. About i860 a sport arose (from seed) which had a 

 pinnate or "fern" leaf. The palmate form is dominant, and the fern 

 leaf is recessive. 



The deformed "Snapdragon" variety of sweet pea behaves as a 

 recessive to the normal type. 



The 2-row barley has certain lateral flowers which are exclusively 

 staminate; in 6-row barley all the flowers are staminate and pistillate, 

 and all set seed. Mr. Biffen crossed these forms, and found that the 

 more negative character was dominant. The offspring were 2-rowed. 



Maize. — When the common or starchy round-seeded maize is 

 crossed with the wrinkled-seeded sugar-maize, the round starchy char- 

 acter dominates. When an egg-cell of the wrinkled sugar-maize stock 

 is fertilised by a pollen-cell of the round starchy stock, the result is a 

 round seed with starchy endosperm. If this seed is sown, it becomes 

 a plant which, on self-fertilisation, forms a cob with a mixture of 

 round starchy and wrinkled sugary seeds in the ratio 3:1. The 

 wrinkled seeds yield sugar-maize; the round seeds yield two "impure 

 rounds" to one "pure round." Correns has observed a very inter- 

 esting case in which two pairs of contrasted characters are implicated. 



