276 



FLOWERS 



Fig. 99 A . — Diagram 

 of the seed of violet. 

 The embryo lies in 

 the center. 



chiefly for the reason that pollination is often wrongly 

 called fertilization.) 



One pollen tube can accomplish the fertilization of only 

 one ovule. Since ovaries often contain many ovules, it is 

 evident that many pollen grains are often 

 needed on the same stigma. 



d . Structure of the Ovule. — There is a 

 little opening into the ovule called the 

 micropyle. (The word means little gate.) 

 The pollen tube usually enters through 

 the micropyle. This little opening may 

 sometimes be seen in mature seeds. In 

 a bean it has the appearance of a hole 

 made with the point of a pin. 

 The micropyle leads to the central part of the ovule, 

 which is called the nucellus. It is within the nucellus that 

 the egg-producing generation lies embedded. (See Figure 

 q$.) The tissue around the nucellus forms a sort of coat 

 called the integument; sometimes there is one integument, 

 sometimes two. 



D. The Receptacle. — That part of the stem from which 

 the parts of the flower arise is called the receptacle. The 

 receptacle is really a part of the flower. In some flowers 

 the ovary, and even parts of the calyx and corolla, appear 

 to be formed by the receptacle. It is often hard to tell 

 where the receptacle ends and the other parts begin. 



If we regard sepals, petals, stamens, and carpels as 

 modified leaves, evidently we may regard the whole flower 

 as a modified shoot, the receptacle being the stem part. 



62. Variations in Structure. — You yourself have noticed 

 that there are many kinds of flowers. There are thousands 



