82 



PLANT BIOLOGY 



FIG. 31. Hind 

 leg of a worker 

 bee. 



thrusts its mouth-parts into the 

 spur as you have just done with 

 the tooth-pick? How are all 

 these parts adapted to hold 

 pollen? (Compare with Figs. 

 30, 31.) 



4. Still holding the pansy in its natural 



position, notice and state the posi- 

 tion of the stigma with reference 

 to the odd petal. 



5. Now push a tooth-pick which has pollen 



on it, a second time into the spur. 

 State whether or not the tooth- 

 pick hits the stigmatic cup before 

 you get it under the stigma. 



6. Why, therefore, will a bee that has just 



been to one pansy flower be almost 

 certain to deposit pollen on the stigmatic cup 

 of the next pansy it visits ? 



7. (Optional home work.) Write a paragraph on "The Visit 

 of a Bee to a Pansy Blossom/' giving a complete 

 account of what the bee does and how it does it. 



94. The advantages of cross-pollination in the pansy. Charles 

 Darwin, the great English biologist, proved by a long series of experi- 

 ments that seeds produced as the result of cross-pollination develop 

 into far more healthy plants than do the seeds which are formed 

 after self-pollination. Among the plants with which he experi- 

 mented was the pansy (Viola tricolor). He planted in each of five 

 pots seeds that had been produced by cross-pollination, and an equal 

 number of seeds that were the result of self-pollination. The results 

 of the experiments are given in his own words as follows: "The 

 average height of the fourteen crossed plants is here 5.58 inches, 

 and that of the fourteen self-fertilized 2.37; or as 100 to 42. In 

 four of the five pots, a crossed plant flowered before any one of the 

 self-fertilized ; as likewise occurred with the pair raised during the 

 previous year. These plants without being disturbed were now 



