MENDEL’S LAWS OF HEREDITY 393 
ILLUSTRATIONS OF SIMPLE MENDELIAN INHERITANCE IN 
BOTH ANIMALS AND PLANTS? 
J. ARTHUR THOMSON 
How far has Mendel’s experience been confirmed?—There has 
been confirmatory work by Correns (on peas, maize, and garden- 
stock), by Tschermak (on peas), by De Vries (on maize, etc.), by 
Bateson and his collaborators (on a large variety of organisms), by 
Darbishire (on mice), by Hurst (on rabbits), by Toyama (on silk- 
moths), by Davenport (on poultry), and so on. There are some 
difficulties and not a few discrepancies, but, as Bateson says, “the 
truth of the law enunciated by Mendel is now established for a large 
number of cases of most dissimilar characters.” 
In experimenting with Lychnis, Atropa, and Datura, Bateson and 
Saunders found that the phenomena conformed with Mendel’s law 
“with considerable accuracy, and no exceptions that do not appear to 
be merely fortuitous were discovered. In the case of Matthiola 
(garden-stock), the phenomena are much more complex. There are 
simple cases which follow Mendelian principles, but others of various 
kinds which apparently do not. The latter cases fall into fairly defin- 
ite groups, but their nature is obscure.” 
In experiments with poultry, the phenomena of dominance and 
recession were detected; interbreeding of the hybrid offspring resulted 
in a mixed progeny, “some presenting the dominant, others the reces- 
sive character, in proportions following Mendel’s Law with fair con- 
sistency, though in certain cases disturbing factors are to be suspected.” 
The general result, so far, is that Mendel’s law has received con- 
firmation in a number of very dissimilar cases. 
Dominant and recessive characters.—Let us first of all collect a 
number of instances of contrasted characters which behave in relation 
to one another as dominants and recessives. 
Dominant Recessive 
Pisum sativum. .... 0.00005 Tallness Dwarfness 
Round seeds Wrinkled seeds 
Coloured seed-coats White seed-coats 
Yellow albumen in coty- Green albumen in coty- 
ledons_. ledons 
Purple flowers White flowers 
Sweet pea.............0005 Tall ordinary form Dwarf or “cupid” vari- 
ety 
*From J. Arthur Thomson, Heredity (copyright 1907). Used by special 
permission of the publisher, John Murray, London. 
