Conditions of life, changed, effect of, ii. [418]-[419];
on horses, i. 52;
upon variation in pigeons, i. 212-213;
upon wheat, i. 315-316;
upon trees, i. 361;
in producing bud-variation, i. 408;
advantages of, ii. [145]-[148], [176]-[177];
sterility caused by, ii. [148]-[165];