302 ESSAYS ON WHEAT 



remains open for only about a quarter of an hour but tbat 

 the flowering period for a whole head has a duration of 

 four days, so that only a small number of flowers are found 

 open at any one time.^^ It has been noticed by many 

 observers that, in a single head, the first flowers to open 

 are the median ones and that flowering proceeds upwards 

 and downwards in the head, the last flowers to open being 

 those in the spikelets at the head's extreme ends. 



Kirchner's observations support those of Delphino, and 

 are as follows: The flowers which are homogamous, 

 gradually open so widely that the tips of the glumes are 

 about 4 mm (% inch) apart. As a flower opens, the an- 

 thers of the stamens dehisce apically and about one^third 

 of the pollen falls into the flower. After this the anthers 

 come to project outside the glumes so that they scatter 

 their pollen into the air. Self-pollination therefore takes 

 place regularly but cross-pollination by means of the wind 

 is not excluded. Kirchner also observed that the flowering 

 period for a single head was four days in length.^^ 



Godron found that the flowers open in the early morn- 

 ing and that the extent of their opening depends upon 

 weather conditions. His observations were as follows: 

 At 16C. (61F.) the flowers open at 4.30 a. m. and close 

 again at 6.30 to 7 a. m. If, when tbe flower opens, the 

 anthers tip over the ends of the glumes quickly, the 

 stigmas of the flowers as a rule are not dusted with pollen. 

 Under less favorable circumstances, the flower opens more 

 slowly and the stigmas do not project until they have been 

 dusted with pollen from the same flower. At a low tem- 

 perature, 12-13C. (54-56F.), or after several days' 

 rain, the flowers remain closed and fertilization takes 



21 Ibid. 



22 lUd. 



