WBAT IS A FLOWSBt CONCLUDED 135 



146. The outer row of the floral envelope or 

 perianth comprises four smaller and greenish parts, 

 which, individually, are known as sepals, and col- 

 lectively as calyx. The calyx, corolla and stamens 

 fall away and perish ; and only the pistil matures 

 into another member. 



XXIV. WHAT IS A FLOWER? CONCLUDED 



147. If the pupil were to cut oflE the anthers 

 before they open and discharge the pollen, and 

 were then to cover the flower with a paper bag, 

 or were to remove all other mustard flowers from 

 the neighborhood, the pistil would soon die and 

 fall. No seeds would be borne. It is, therefore, 

 certain that the pollen is in some intimate way 

 associated with the production of the seed. 



148. If, however, having done this, the pupil 

 were to bring pollen from another mustard flower 

 and deposit it upon the stigma, he would find 

 the pistil maturing and the seeds forming, as if 

 he had not interfered with the flower. It is evi- 

 dent, therefore, that the office of the pollen is to 

 cause production of seed by some action which it 

 exerts after it is applied to the pistil. This action 

 upon the forming seed is known as fertilization ; and 

 the transfer of the pollen to the stigma (whether 



