THE ORGANIZATION OF THE PLANT 



79 



FIG. 68. A typical mono- 

 cotyledon flower 



respectively the sepals, petals, stamens, and carpels. On the 

 outside are the green and leaf like sepals ; next within are the 

 colored and more delicate petals; then come one or more 

 circles of threadlike organs with knobbed ends, the stamens; 



and last, occupying the center of the 

 flower, are one or more bottle-shaped 

 or club-shaped carpels. Taken collec- 

 tively, the sepals form the calyx and 

 the petals the corolla. The carpels 

 when united form the pistil, though 

 often the carpels themselves are called 

 pistils. The base of the pistil is the 

 ovary and within it are the ovules, des- 

 tined to ripen into seeds. In order 

 that fertile seeds be produced, however, it is necessary that 

 the flower be pollinated, that is, that the tiny grains of pollen 

 formed in the knobs, or anthers, of the stamen fall upon the 

 stiyma at the apex of the pistil. In this position each grain 

 puts out a pollen tube which grows down through the sub- 

 stance of the pistil until it meets and enters an ovule, after 

 which fertilization, or the union of an 

 egg and sperm, is accomplished. Each 

 flower, therefore, must receive at least 

 as many pollen grains as it ripens 

 seeds, and it usually receives many 

 more, for some fail to reach the stigma 

 and are therefore wasted. The end of 

 the stem, from which the floral parts 

 rise, is called the receptacle. When the 

 other sets of organs in the flower ap- 

 pear to spring from the base of the ovary, the flower is said to 

 be hypogynous. Sometimes the receptacle grows up about the 

 ovary in such a way that the floral parts seem to grow from 

 the top of the ovary. In such cases the flower is epigynous. 



FIG. 



. A typical dicoty- 

 ledon flower 



