TRITICUM 95 



gamy) is the rule in nearly all wheats. Durum wheat, how- 

 ever, has the habit of cross-pollination (xenogamy), and it has 

 been suggested that this behavior is partly responsible for 

 its better adaptation to dry climates, and for its greater dis- 

 ease resistance and vigor. Cross-pollination is quite common 

 in the primitive wheat, which is an inhabitant of a dry, warm 

 country. It appears that cross-pollination is the rule in 

 hot, dry localities, such as certain parts of India. 



Artificial Cross-pollination. — One of the chief means of 

 wheat improvement is hybridization. This necessitates the 

 operation of artificial cross-pollination. In this process, 

 the glumes of the flower of the female parent are spread 

 apart and the three stamens removed; this is done just before 

 the anthers are mature. On the same day, or on the follow- 

 ing morning, pollen is taken from the mature anthers of the 

 plant to serve as the male parent, and placed between the 

 glumes of the flower from which the stamens have been re- 

 moved. The chances are that the pollen will reach the 

 stigma branches of the emasculated flower, germinate, and 

 effect cross-fertilization. 



Fertilization and Maturing of Grain. — Brenchley states 

 that fertilization in wheat normally occurs between one and 

 two days after pollination. This interval represents the 

 time necessary for the pollen grain to germinate, and for the 

 pollen tube to grow down through the stigma to the embryo 

 sac in the developing ovule. This interval no doubt varies 

 in different varieties and under different environmental con- 

 ditions, particularly temperature. Cool weather will retard 

 germination of the grain, and growth of the pollen tube, and 

 thus affect the "setting" of grain. 



After fertilization, the embryo begins to develop, the endo- 

 sperm to store reserve material, and the seed and fruit walls 

 to undergo marked changes. 



