MENDEL’S LAWS OF HEREDITY 395 
One variety, Zea mays alba, which has smooth white seeds, was 
crossed with another variety, Zea mays coeruleodulcis, which has 
wrinkled blue seeds. The hybrids (F,) had smooth blue seeds, one 
character of each parent being dominant, and one character of each 
parent being recessive. The hybrids were inbred, and the progeny 
(F,) showed four combinations—smooth blue, smooth white, wrinkled 
blue, and wrinkled white (the dominant characters are italicised). 
In the next generation (F;), the wrinkled white, inbred, yielded 
wrinkled white—a case of extracted recessives, breeding true. The 
smooth whites and wrinkled blues, inbred, yielded partly forms like 
themselves and partly wrinkled white. The smooth blues, inbred, 
yielded the same combinations as in F;. 
A finer corroboration of Mendelian could hardly be wished. 
Nettles.—Correns crossed two “species of stinging-nettle,” Urtica 
pilulifera L. and U. dodartit L., which resemble one another except as 
regards leaf-margin, strongly dentate in the former, almost entire in 
the latter. The hybrid offspring (F,) have all dentate leaves like the 
male or the female parent, as the case may be. The dentate character 
is absolutely dominant. The inbred (self-fertilised) hybrids produce 
offspring (F,) of two kinds, with dentate and with entire margins, on an 
average in the Mendelian proportion, 3:1. 
“Immunity to rust in wheat.—Some kinds of wheat are very 
susceptible to the fungoid disease known as ‘rust’; others are immune. 
The quality of immunity to rust is recessive to the quality of predis- 
position to rust. ; 
“When an immune and a non-immune strain are crossed together 
the resulting hybrids are all susceptible to ‘rust.’ On self-fertilisation 
such hybrids produce seed from which appear dominant ‘rusts’ and 
recessive immune plants in the expected ratio of 3:1. From this 
simple experiment the phrase ‘resistance to disease’ has acquired a 
more precise significance, and the wide field of research here opened 
up in this connection promises results of the utmost practical as well 
as theoretical importance. To the question, ‘Who can bring a clean 
thing out of an unclean ?’ we are beginning to find an answer, nor is 
the answer the same as that once given by Job” (R. C. Punnett). 
Silkworms.—Toyama paired Siamese silkmoths with yellow or 
with white cocoons; the offspring produced only yellow cocoons. 
When the hybrids were inbred, the result was two sets, one producing 
white cocoons, the other producing yellow cocoons, and the proportion 
was Mendelian—25.037 white and 74.96 yellow. The whites bred 
