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PROPAGATION OF PLANTS BY MEANS OF SEEDS 



There are several distinct plans in nature to prevent self-pol- 

 lination even in flowers which have both essential organs. These 

 plans are to help enforce cross-pollination. 



1. The stamens may scatter their pollen before the pistil is 

 ready to receive pollen. 



2. The pistil may be mature first and may have received its 

 pollen from another flower before the stamens in its own flower 

 have shed any pollen. 



Fig. 7. — Bees aid in pollination of fruit blossoms. A bee hive was placed under this 

 tree at blossom time, thus producing a heavy crop. (California Station.) 



3. In erect flowers, sometimes the stamens are lower than the 

 pistil so the pollen does not fall readily upon the stigma of the pistil. 



4. In flowers which droop, sometimes the stamens are so much 

 longer than the pistil that the pollen falls away from the pistil in- 

 stead of upon it. 



Cross-Pollination. — Not only is cross-pollination necessary in 

 the four plans mentioned above, but also in the many kinds which 

 have the stamens and pistils in separate flowers. 



