VI CONTENTS. 



CONDITIONS OF LIFE — CONTABESCENCE OF THE ANTHERS — MON- 

 STROSITIES AS A CAUSE OF STERILITY DOUBLE FLOWERS— SEED- 

 LESS FRF IT — STERILITY FROM THE EXCESSIVE DEVELOPMENT OF 

 THE ORGANS OF VEGETATION FROM LONG-CONTINUED PROPAGA- 

 TION BY BUDS INCIPIENT STERILITY THE PRIMARY CAUSE OF 



DOUBLE FLOWERS AND SEEDLESS FRUIT .. .. Pages 127-156 



CHAPTER XIX. 



SUMMARY OF THE FOUR LAST CHAPTERS, "WITH REMARKS 

 ON HYBRIDISM. 



ON THE EFFECTS OF CROSSLNG THE INFLUENCE OF DOMESTICATION 



ON FERTILITY — CLOSE INTERBREEDING — GOOD AND EVIL RESULTS 

 FROM CHANGED CONDITIONS OF LIFE — VARIETIES WHEN CROSSED 

 NOT INVARIABLY FERTILE ON THE DIFFERENCE IN FERTILITY BE- 

 TWEEN CROSSED SPECIES AND VARIETIES — CONCLUSIONS WITH RE- 

 SPECT TO HYBRIDISM LIGHT THROWN ON HYBRIDISM BY THE 



ILLEGITIMATE PROGENY OF HETEROSTYLED PLANTS — STERILITY 

 OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE 

 REPRODUCTIVE SYSTEM — NOT ACCUMULATED THROUGH NATURAL 

 SELECTION — REASONS WHY DOMESTIC VARIETIES ARE NOT MUTUALLY 

 STERILE — TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE 

 IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES 

 — CONCLUSION 157-175 



CHAPTER XX. 



SELECTION BY MAN. 



SELECTION A DIFFICULT ART — METHODICAL, UNCONSCIOUS, AND NATURAL 



SELECTION RESULTS OF METHODICAL SELECTION — CARE TAKEN IN 



SELECTION — SELECTION WITH PLANTS — SELECTION CARRIED ON BY 



THE ANCIENTS AND BY SEMI-CIVILISED PEOPLE UNIMPORTANT 



CHARACTERS OFTEN ATTENDED TO — UNCONSCIOUS SELECTION AS 



CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED 

 ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS SELEC- 

 TION — INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB- 



