494 Introduction to the Study of Science 



Observe landing places when present in flowers ; note where these are 

 placed in relation to stigmas and anthers ; whether they have any 

 other uses than merely as landing places for insects. 



(a) Many blossoms, as those of the pear and apple, have a different 

 way of securing cross-pollination. The stigmas mature and are 

 ready for the pollen before the pollen is ripe. This necessitates trans- 

 fer of pollen from other blossoms. 



(6) In blossoms of certain plants, such as the bean, daisy, and 

 sunflower, the pollen grains ripen and are dispersed before the stigmas 

 are receptive. These points are important in the production of new 

 varieties by hand-pollination. 



Observe the structure of such flowers as the cowslip, primrose, and 

 blue flag, which have an arrangement of stamens and anthers with 

 relation to the stigmas, that makes cross-pollination necessary, and 

 close-pollination almost impossible. 



Study the ways in which different insects, bees, moths, and butter- 

 flies, obtain the nectar and collect pollen. Examine typical insects, 

 their bodies, legs, wings, heads, and mouth parts. 



SUMMARY 

 The parts of a complete flower are : 



Floral envelope, 



Sepals, constituting the calyx, 

 Petals, constituting the corolla. 



Essential organs, 



Stamens, producing pollen, 

 Pistils, producing ovules. 



Pollination is the transfer of pollen grains from the anthers of the 

 stamens to the stigma of the pistil. 



Fertilization consists of the union of the nucleus of the pollen grain 

 with the nucleus of the ovum. 



The fertilized ovum, using nutriment from the sap of the parent, 

 develops into a seed, which consists of an embryo plant, a supply of 

 nutritive material, and a protective covering. 



Flowers that have stamens but not pistils are staminate. Flowers 

 that have pistils but not stamens are pistillate. Those possessing both 

 sets of organs are perfect flowers. 



Cucumber vines and plants of corn have both staminate and pis- 

 tillate flowers. 



