CHAPTER 2.XXII.--CAUSES OF VARIABILITY.

VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES ASSIGNED BY
VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF EVERY KIND DUE TO
CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH CHANGES--CLIMATE, FOOD,
EXCESS OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS OF GRAFTING ON THE
VARIABILITY OF SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO
CHANGED CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE
INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE VARIABILITY
--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW CHARACTERS--VARIABILITY FROM
THE COMMINGLING OF CHARACTERS AND FROM REVERSION--ON THE MANNER AND PERIOD OF
ACTION OF THE CAUSES WHICH EITHER DIRECTLY, OR INDIRECTLY THROUGH THE
REPRODUCTIVE SYSTEM, INDUCE VARIABILITY.




CHAPTER 2.XXIII.--DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF
LIFE.

SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS,
IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES--LOCAL
DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC.--
PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF
POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE
THROUGH THE DEFINITE ACTION OF EXTERNAL CONDITIONS--COMPARISON OF AMERICAN AND
EUROPEAN TREES--GALLS--EFFECTS OF PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO
THE BELIEF IN THE POTENT INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL
SERIES OF VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE