GRASSES OF IOWA. 53 



manner in which grama grass, Bouteloua oUgostachya is pol- 

 linated. 



The plants grow closely intermingled, forming a dense, soft 

 mat a few inches in height. The flowers are arranged in one- 

 sided spikes, of which there are usually two or three. The 

 two stigmas protrude from the base of the partially opened 

 glumes and recurve towards the main rachis. The anthers, as 

 is usual in grasses, hang on slender filaments, easily shaken 

 by the slightest breeze. The spikes are so arranged that 

 when acted upon by the wind they turn like vanes. This 

 brings all the spikes in a direction nearly parallel to the wind, 

 the stigmas being to the windward and the anthers to the lee- 

 ward; thus the stigmas necessarily receive pollen from a dif- 

 ferent plant. The same adaptation is seen in other species of 

 Bouteloua and in some other grasses. 



Many of the flowers of grasses have a pair of small scales, 

 physiologically of great importance, as they assist in the 

 pollination of grasses. The bases of these lodicules are 

 grown together. The rapid swelling of the bases at least 

 causes the separation of the flowering glume and palet, and 

 hence the opening of the flower. These turgid scales may 

 be seen at the time of flowering in many grasses. They are 

 very evident in Poa arachnifera, Panicum miliaceum, Avena 

 sativa, Bromus mollis and Festuca elatior. In grasses where 

 these scales swell but little, the flowers do not open very far. 

 Where they are absent the spikelets are closed at the sides 

 and the stamens and pistil only protrude at the apex. The 

 time of opening of grasses in different genera varies greatly. 

 It is well known that temperature and moisture greatly influ- 

 ence the opening of flowers. Rain and low temperature may 

 retard the opening, not only hours but days. Dry air and a 

 high temperature also retard opening. The flowers of grasses 

 open, as a rule, early in the morning, usually when there is 

 some dew. Festuca pratensis opens before 7 a. m. Mr. P. A. 

 Sirrine found that about Ames the flowers of grasses usually 

 open between 5 and 9 a. m. Some, however, open between 5 

 and 7 p. M. Kerner von Marilaun* states 4 to 5 a. m. for Poa 

 and Koeleria; 5 to 6 a. m. for Brazia media, Aira ccespitosa, 

 wheat and barley. Rye, 9 a. m. This is, however, not always 

 the case in cereals, as they may open at any time of the day. 



* Pflanzenleben. 2: 139. 



