eneration to another; the question was, Why do they vary? and
do these variations really represent new characters comparable to new
species in the making? or are they, so to speak, but an elastic reaction
of the internal vital elasticity of the organism, all the while latent
and only seeking a favorable expression, to return again under other
conditions to the former type?

The effort to reduce these variations to law and system was pursued by
thousands of investigators, with varying but at all times perplexing
and disappointing results. But in the year 1900 the scientific world
awoke to the surprising fact that a patient obscure investigator had
already solved most of the puzzles of variation and heredity some
thirty-five years before. Gregor Mendel, born a peasant boy, trained as
a monk, and afterwards appointed Abbot of Bruenn, had in the year 1865
published the results of his experiments in breeding, which had been
ignored or forgotten until rediscovered in 1900 by de Vries and two
others simultaneously. From this point Mendelism, as it is now called,
has steadily gained ground, until at the present time it can be said to
be the dominating conception among biologists the world over regarding
the problems of heredity.

Mendel worked chiefly with peas, crossing different varieties. In his
methods of investigation he differed from all previous investigators in
concentrating his attention upon a single pair of alternative or
contrasted characters at a time, and observing how these alternative
characters are transmitted.

Thus when he crossed a tall with a dwarf, giving attention to this pair
of contrasted characters alone, he found that all the first hybrid
generation were talls, with no dwarfs and no intermediates. Accordingly
he called the tall character _dominant_, and the dwarf character
_recessive_, and a pair of contrasted characters which act in this way
are now called _factors_ or sometimes called _unit characters_. But on
allowing these hybrids to cross-fertilize one another in the usual way,
Mendel found that in the second generation of hybrids there were
_always_ _three talls to one dwarf_ out of every four. Further
experiments proved that these dwarfs of the second hybrid generation
_always bred true_, that is, one out of four; and that one out of the
remaining talls always bred true, making another quarter of the total;
while the remaining fifty per cent. proved to be mixed tails, always
acting as did th