CHAPTER XVI. 



THE PHYSIOLOGY OF THE FLOWER. 



Primary functions To produce pollen and embryo-sac, &c. 

 and to ensure fertilisation and the nursing of the embryo 

 Prevention of self-pollination Adaptations for cross-pollination 

 DicEcism and Moncecism Polygamy Hydrophily Anemo- 

 pliily Entomophily Hermaphrodite or Monoclinous Flowers 

 Proterogynj^ and Protandry Dichogamy and Autogamy 

 Abortion of Stamens Barren pollen Pseudo-hermaphrodite 

 flowers Gynodioecism, &c. 



The functions of a flower are, primarily, to produce the 

 pollen-sacs and pollen, and the ovules and embryo-sac 

 with their contents ; and to ensure that the pollen-grains 

 reach the stigmas or ovules, and that the latter are nursed 

 until they develope into ripe seeds in the fruit. 



The primary function of course depends on the fact 

 that the flower consists essentially of sporophylls stamens 

 and carpels in which sporangia and spores are developed ; 

 but, since it is necessary for the pollen-grains (microspores) 

 to germinate on the stigma or on the micropyle, in order 

 that the pollen-tube may reach the embryo-sac (macro- 

 spore), it is obvious that in the frequent cases where 

 stamens and pistil are on separate plants or flowers, some 

 contrivance for conveying the pollen must exist, e.g. in 

 Pines, Willows, Birches, Oaks, Beech, Chestnut, Hazel, &c. 



