SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.
ON THE EFFECTS OF CROSSING--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 BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS
WITH RESPECT TO HYBRIDISM--LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE
PROGENY OF DIMORPHIC AND TRIMORPHIC 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 ... Page 173