BIOLOGY OF THE FLOWER 159 



pistil may be distinguished : (1) the ovary, within which 

 the ovules are developed ; (2) the style, growing from the 

 top of the ovary and ending in (3), a stigma which, when 

 ripe, is coated with a sticky sugary secretion. To this the 

 pollen-grains adhere and germinate. The ovules, after 

 fertilization by the pollen, undergo changes which result 

 in the formation of seeds. Each ovule or megasporangium 

 (Gr. megas = large) contains a megaspore (the embryo 

 sac), and the sporophylls which bear them are known as 

 megasporophylls. 



The essential work of the flower is to secure the trans- 

 mission of pollen-grains from the stamens to the stigmas, 

 a process known as pollination, so that fertilization of the 

 ovules may occur and seeds be formed. The flowers of 

 different plants vary considerably in structure according 

 to the way in which pollen is conveyed. It may be carried 

 by the wind or by insects, or the arrangement and be- 

 haviour of the parts may be such as to transfer pollen from 

 the anthers to the stigmas of the same flower. If we 

 examine a number of common flowers from this point of 

 view, we shall learn much of their structure and modifica- 

 tions, and also of their special use to the plant. Each 

 flower should be carefully examined, and floral diagrams 

 and drawings made to show the relationships of the parts, 

 especially as seen in a vertical section. 



Flowers pollinated through the agency of wind. The 

 flowers of the Hazel or Oak (Figs. 187 and 194) are arranged 

 in a catkin. Each flower of the long yellow catkin is much 

 smaller than that of the Stock ; outside are five or seven 

 green scales ; within are five to twelve stamens, but no 

 pistil and no corolla are present. The flowers in the smaller 

 bud-like catkins have six small scales on the top of an 

 ovary with three chambers, and there are three large sticky 

 stigmas to catch the pollen. From these flowers both 

 stamens and corolla are absent. 



