CONTENTS. VU 



and self-furtilised offspring when again crossed and self-fertilised 



Comparison of the fertility of flowers fertilised with their 

 own pollen and with that from other flowers on the same plant 



Self-sterile plants Causes of self-sterility The appearance 

 of highly self-fertile varieties Self-fertilisation apparently in 

 some respects beneficial, independently of the assured produc- 

 tion of seeds Relative weights and rates of germination of 

 seeds from crossed and self-fertilised flowers .. Page 312-355 



CHAPTER X. 



Means of Febtilisatton. 



Sterility and fertility of plants when insects are excluded The 

 means by which flowers are cross-fertilised Structures favour- 

 able to self-fertilisation Relation between the structure and 

 conspicuousness of flowers, the visits of insects, and the advan- 

 tages of cross-fertilisation The means by which flowers are 

 fertilised with pollen from a distinct plant Greater fertilising 

 power of such pollen Anemophilous species Conversion of 

 anemophilous species into entomophilous Origin of nectar 

 Anemophilous plants generally have their sexes separated 

 Conversion of diclinous into hermaphrodite flowers Trees 

 often have their sexes separated 356-417 



CHAPTER XL 



The Habits of Insects in eelation to the Febtilisation 



of Flowebs. 



[nsects visit the flowers of the same species as long as they can 

 Cause of this habit Means by which bees recognise the 

 flowers of the same species Sudden secretion of nectar 

 Nectar of certain flowers unattractive to certain insects In- 

 dustry of bees, and the number of flowers visited within a short 

 time Perforation of the corolla by bees Skill shown in the 

 operation Hive-bees profit by the holes made by humble-bees 

 Effects of habit The motive for perforating flowers to save 

 time Flowers growing in crowded masses chiefly perforated. 



418^38 



