VI 



CONTENTS OF VOL. II. 



CHAPTER XXI 



SELECTION — continued. 



NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS — CHARACTERS WHICH 



APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE 



CIRCUMSTANCES 



FAVOURABLE TO SELECTION BY MAN — FACILITY IN PREVENTING CROSSES, AND 



NATURE 



CLOSE ATTENTION AND PERSEVERANCE INDIS- 



PENSABLE — THE PRODUCTION OF A LARGE NUMBER OF INDIVIDUALS ESPECIALLY 



FAVOURABLE 



WHEN NO SELECTION IS APPLIED, DISTINCT RACES ARE NOT FORMED 



HIGHLY-BRED ANIMALS LIABLE TO DEGENERATION 



TENDENCY IN MAN TO 



CARRY THE SELECTION OF EACH CHARACTER TO AN EXTREME POINT, LEADING TO 



DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE — CHARACTERS CONTINUING 

 TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE ALREADY VARIED — 

 DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE VARIETIES, 



LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES 



LIMIT TO THE POWER OF 



SELECTION 



LAPSE OF TIME IMPORTANT 



MANNER IN WHICH DOMESTIC RACES 



HAVE ORIGINATED 



summary . . Page 224 







CHAPTER XXII 



CAUSES OF VARIABILITY. 



VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION — CAUSES ASSIGNED 

 BY VARIOUS AUTHORS — INDIVIDUAL DIFFERENCES VARIABILITY OF EVERY KIND 



ON THE NATURE OF SUCH CHANGES 



SLIGHT CHANGES SUFFICENT 



EFFECTS 



DUE TO CHANGED CONDITIONS OF LIFE - 



CLIMATE, FOOD, EXCESS OF NUTRIMENT — 



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 APPEAR- 



ANCE 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 



250 



CHAPTER XXIIL 



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 



HE 



EFFECTS OF PARASITIC FUNGI 



THE POTENT INFLUENCE OF CHANGED EXTERNAL CONDITIONS — PARALLEL SERIES 



OF VARIETIES 



OF CHANGE IN THE CONDITIONS 



AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE 



BUD-VARIATION — MONSTROSITIES PRODUCED 



BY UNNATURAL TREATMENT 



SUMMARY 



271 



