EXERCISE 49 

 PREVENTION OF SELF-POLLINATION BY DICHOGAMY 



Materials. Flowers in the field, or, if necessary, the flowers may 

 be brought into the laboratory. 



Directions for work. By dichogamy is meant the maturing of 

 stamens and stigma in a flower at different times. The maturity 

 of the stamen may be judged by the shedding of the pollen ; 

 most stigmas have a moist surface at the time that the pistil is 

 ready for pollination. If the stamens mature first, the pollen 

 will have fallen before the stigma is in a receptive condition ; 

 if the stigma matures first, it usually will have been pollinated 

 by pollen from other flowers before the stamens in the same 

 flower have shed their pollen. Obviously, in either case effec- 

 tive self-pollination will be impossible or highly improbable. 



Examine all the flowers available and list them below, indi- 

 cating, by check mark in the proper column, to which of the 

 three classes they belong: 



References 



BERGEN and CALDWELL. Practical Botany, pp. 131, 132. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 152, 153. 

 LUBBOCK. Flowers, Fruits, and Leaves, chap. ii. The Macmillan 

 Company. 



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