Many flowering plants have only stamens or pistil in a 

 flower, not both, and the staminate and pistillate flowers 

 may be on one plant or separate ones. This obviously 

 necessitates the arrival of pollen from another flower or 

 plant, in order to fertilise the ovules. This is called cross- 

 fertilisation, to distinguish it from self -fertilisation . 

 When both organs are formed in the same flower it is very 

 common for special contrivance to exist, to prevent self 

 and compel cross -fertilisation. 



When flowers are small, dingy, and odourless, cross- 

 fertilisation is effected by pollen being carried by currents 

 of air from the anther to the stigma. This may be 

 observed in grasses and Sheoak. When flowers are brightly 

 coloured or scented, insects visit them in quest of honey, or 

 to gather pollen for food. An insect cannot travel about 

 an open flower without getting dusted with pollen, some 

 of which it will probably leave on the stigma of the next 

 flower it visits. 



