52 



GRASSES OF IOWA. 



readily receive the pollen. Self-pollination can occur in many 

 grasses as stamens and pistils mature at the same time, but 

 this is prevented in tall meadow oat 'grass and others by the 

 difference in time in which stamens and pistils mature. In 

 this grass the pistil matures first and is therefore protero- 

 gynous. When the pollen is mature and is shed, the stigmas 

 have wilted and are no longer in a r3ceptive caditi on. In 

 most grasses stamens mature first and the tiowers are pro- 

 terandous. 



The flowers of our Andropogon provincialis with digitate 

 spikes are gently blown by the wind. When they come in 

 contact with a neighboring plant they are sure to leave some 

 of the pollen on the receptive stigma. The long, purple plu- 

 mose stigma is proterogynous, and therefore not ready to 

 receive the pollen when the stamens dehisce. The flowers 

 open during the early morning (5 a. m.), when there is consid- 

 erable dew on the ground. 



Professor Hitchcock* has described quite interestingly the 



Fig. 43. The opening of grass-flowers. Beginning to the left: Tall Meadow Oat grass, 4rr/ien- 

 atherumavenaceum; Men-dow Fox- tBiil, AlopecurtLS pracensis; Hungarian Brome, Bromiw fjiernife," Rye, 

 Secale cereale ; Meadow Fescue, Festuca pratensis. 



•Report on a collection of plants made by C. H. Thompson in southwestern Kansas 

 in 1893. Oontr. U. S. Nat. Herb., 3: 537. 



