394 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



Dominant Recessive 



Stocks Coloured WOiite 



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 pilulijera and 



U. dodartii) Serrate leaf margin Entire leaf margin 



Mirabilis jolapa 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 imphcated. 



