THE CYCLE OF LIFE : FLOWERS 45 



a baby plant, or embryo. The surrounding walls of the ovule 

 become the seed coats. The ovule, with its embryo sac, thus 

 changes into a seed. In addition to the food used by the embryo 

 in its development and growth the parent plant supplies other 

 food materials. These are accumulated either immediately 

 around the embryo or within the embryo itself. After the seed 

 sprouts and before it is able to supply itself the young plant 

 uses this surplus food. 



Fertilization brings about changes in other parts of the flower. 

 The petals drop off, and usually the stamens also. The ovary 

 begins to enlarge and at last ripens into the central or even the 

 entire body of the fruit.^ In some plants the calyx of the flower, 

 and even the enlarged end of the stalk, the receptacle, may be- 

 come fused into the fleshy fruit. 



37. Pollenation. In many plants the pollen is carried from 

 the stamen to the stigma by the growth movements of the parts 

 of the flower. The style, as it gets longer, may bring the stigma 

 into contact with the anther ; or the corolla, as it grows and 

 opens, pushes the stamen against the stigma; or the stalk of 

 the flower may bend over as it grows, and so deposit some of 

 the pollen from the anther on the stigma. In some flowers the 

 anther stands above the stigma, and the pollen is carried over 

 by the action of gravity. Thus there are many kinds of plants 

 in which the flower may be said to pollenate itself. This process 

 is sometimes called close-pollenation. There are many plants, 

 however, in which close-pollenation is quite impossible. 



I. Space relations. The position of the stamen in relation to 

 the pistil may make close-pollenation impossible, as in the iris, 

 or blue flag, in the milkweed, in all the orchids, and in many 

 other groups of plants. In some species there are two kinds of 



iJn most of the common plants the fruit will not ripen (that is, the ovary 

 will not continue its development) unless fertilization takes place. But there 

 are many plants in which a seedless fruit is possible. Seedless oranges, seed- 

 less apples, seedless grapes, the pineapple, and the banana are examples of 

 fruits that develop without the ovule being first fertilized. The plantain and 

 the breadfruit develop a more juicy fruit when there is no fertilization. 



