CONTROLLING POLLINATION 69 



1910c). After becoming familiar with the flower structure it 

 is important to determine at what time of day the pollen is 

 most easily collected and for what length of time the stigma is 

 receptive. Environmental conditions modify the expression 

 of these and other characters. However, some general rules 

 for different groups of crops may be given. 



Certain tools are essential for the work of pollination. For 

 general work these are a small pair of thin, pointed scissors; a 

 pair of forceps with thin, pointed blades which meet exactly 

 and which are not too stiff; one or two dissecting needles; a 

 hand lens; a pencil; and small string tags for recording purposes. 

 Other special apparatus is necessary for difficult crosses. 



Crossing of Small Grains. The technic of small grain crossing 

 is comparatively simple. Some practice, however, is necessary 

 in order to gain proficiency and to obtain a fair percentage of 

 seeds set. In some of the earlier directions it was stated (Hays, 

 1901) that it was necessary to make crosses of wheat at about 

 4 o'clock in the morning. Leighty and Hutcheson (1919) have 

 determined the period in which blooming takes place at Univer- 

 sity Farm, St. Paul, Minn., and at Arlington Farm, Rosslyn, 

 Va. The spikes were examined at 7 a.m., 12 n., and 5 or 6 p.m. 

 A flower was considered as having bloomed when the glumes 

 had opened appreciably. The period from 5 or 6 p.m., to 7 

 or 8 a.m. was referred to as night. Of 2,977 wheat flowers on 

 69 spikes, 1,492 bloomed at night and 1,485 bloomed during the 

 day. About half of those which bloomed during the day bloomed 

 before noon. These figures are given to correct the erroneous 

 idea that it is always necessary to pollinate wheat early in the 

 morning. Environmental conditions may be an important 

 factor, for Salmon (1914), working in South Dakota, stated 

 that blooming was practically completed before 7 o'clock in the 

 morning. 



Leighty and Hutcheson (1919) show that in wheat it is unsafe 

 to leave the spikes uncovered after emasculation. Seeds were 

 formed by 507 of 1,240 emasculated, unprotected flowers at 

 University Farm, Minn, and 1,103 seeds were formed in 1,324 

 flowers similarly handled at Arlington Farm, Va. while less than 1 

 per cent, of flowers emasculated and covered with paper bags set 

 seed. Frear (1915) , working with Turkey winter wheat, obtained 

 80 per cent, seeds set on emasculated, uncovered spikes and less 

 than 1 per cent, on emasculated covered spikes. 



