298 PLANTS 



The stamen consists of two distinct parts : the stalk, or filament, 

 and the pollen case, or anther. In flowers that have the corolla in one 

 piece the stamens are often attached to the corolla. 



The carpel of an ordinary flower consists, first, of a bulb-like seed 

 case, or ovary, in which tiny ovules, or " little eggs," are produced. 

 Above the ovary is a solid stem, called the style, which looks like the 

 neck of a flask. The tip of the style bears a sticky, outspread surface, 

 called the stigma. In many plants two or more of the carpels are 

 united, so that all the ovules are in one ovary. We call the whole 

 group of carpels the pistil. Thus, a simple pistil has only one carpel; a 

 compound pistil consists of two or more carpels. 



The number of parts in flowers is important. Thus, there are usu- 

 ally 3 or 5 sepals, petals, stamens, and carpels. Often, however, the 

 number of stamens is twice that of the sepals. The number of petals 

 is also frequently doubled. The buttercup has 5 sepals, 5 petals, and 

 often over 30 stamens. In many flowers petals, or sepals, or both, are 

 entirely wanting. 



319. Formation of Seeds. The structure of a seed 

 has been given in 307 and 308; let us now learn how 

 seeds are formed. Before the ovule in the carpel can 

 become a seed, it must be fertilized by the pollen. When 

 the flower is mature, the pollen case splits, or breaks 

 open, and the pollen grains are carried by the wind or 

 by insects to the sticky surface of the stigma. Here the 

 pollen grain sends out a long tube that carries the fertilizing 

 pollen cells. The tube passes through the style into the 

 ovary, and then into the ovule. When the pollen tube 

 reaches the ovum, or i i egg," within the ovule, the pollen cell 

 and ovum unite. The addition of the pollen cell to the 

 ovum causes the ovum to develop very rapidly, and it be- 

 comes the embryo (cf. 307). The ovule forms a hard coat 

 (testa) about the embryo, and any vacant space is stuffed 

 with food. The completely prepared ovule is then a seed. 



