74 THE PRINCIPLES OF AGRICULTURE. 



The essential parts of a flower are the central, or in- 

 terior organs, by which the seeds are formed. These are 

 generally surrounded by floral envelopes, called the calyx 

 and the corolla, whose individual leaves, the sepals and 

 petals, give the flower its beauty. 



The central organs are of two kinds, called pistils and 

 stamens. 



The pistils contain germs from which seeds are formed, 

 and the stamens produce a fine dust, generally of a yel- 

 low color, called pollen. 



This pollen, falling upon the pistils, fertilizes them, 

 and starts the formation of seeds. 



Usually both stamens and pistils grow upon the same 

 plant, and near each other in the same flower. In some 

 varieties, however, the pistils are borne upon one plant 

 and the stamens upon another. This is true of some 

 varieties of strawberries, and of hop and hemp plants. 



On account of this peculiarity, it is necessary, in culti- 

 vating these crops, to mix plants of both kinds. 



Sometimes the pistils are borne upon one part of a 

 plant, and the stamens upon another. An example of 

 this is seen in Indian corn. The pollen produced upon 

 the tassel falls upon the silk, which is connected with 

 the pistils within the ear. 



Pollen dust is produced by some plants in large quan- 

 tities, and is carried long distances by the wind. This, 

 falling upon different plants of the same species, causes 

 a mixture. 



By a transfer of pollen dust in this way, an almost 

 endless variety of some species of plants is obtained. 

 A green variety of squashes growing beside a yellow 

 variety yields a variety partly green and partly yellow. 

 Grains of pollen dust, carried by the wind from one corn- 



