XIV CONTENTS. 



CHAPTER IX. 



GRADATION Or OBGAKS, &C. — CONCLUDING REMARKS. 



Gradation of organs, of the rostelliini, of the jjollen-masses — 

 Formation of the cavidicle — Genealogical afiinities — Secretion 

 of nectar — Mechanism of the movement of the pollinia — Uses 

 of the petals — Production of seed — Importance of trifling 

 details of structure — Cause of the great diversity of structure in 

 the flowers of Orchids — Cause of the perfection of the con- 

 trivances — Summary on insect-agency — Nature abliors per- 

 petual self- fertilisation Page 247-293 



Index 294 



