CHAPTER VIII.

DIFFERENCE BETWEEN CROSSED AND SELF-FERTILISED PLANTS IN CONSTITUTIONAL VIGOUR AND IN OTHER RESPECTS.

Greater constitutional vigour of crossed plants.--The effects of great crowding.--Competition with other kinds of plants.--Self-fertilised plants more liable to premature death.--Crossed plants generally flower before the self-fertilised.--Negative effects of intercrossing flowers on the same plant.--Cases described.--Transmission of the good effects of a cross to later generations.--Effects of crossing plants of closely related parentage.--Uniform colour of the flowers on plants self-fertilised during several generations and cultivated under similar conditions.