68 BREEDING CROP PLANTS 



Two men may well work together in pollination. One unties 

 the ear bag and the other shakes the dead anthers from the 

 tassel bag and pours the pollen over the silk. Care is needed 

 in performing this operation to prevent cross- or uncontrolled 

 pollination. In producing biotypes by self-fertilization the 

 occasional cross may easily be rogued out as the crossed plant 

 will plainly be seen the following year because of its vigor and 

 other characters. Some workers prefer transparent paper bags 

 .which allow the development of the silks to be noted without 

 removing the bag from the ear, and thus save unnecessary work. 



Hard showers or long continued rains seriously interfere with 

 the artificial pollination of corn, as the tassel bag becomes wet 

 and makes the handling of the pollen difficult. A desirable 

 method is to remove the tassel bags after each rain and put on 

 new ones. As a number of days elapse from the time the first 

 pollen of the tassel matures until all is mature, the method 

 of replacing tassel bags gives good results. 



Self-pollination of squash has been carried out at the 

 Minnesota Station. A little practice helps in determining when 

 a flower is about ready to open. The petals of both staminate 

 and pistillate flowers are prevented from opening by placing a 

 small rubber band around each one. On removing the band the 

 following day the flower quickly opens if it is ready for pollina- 

 tion. The petals are then removed from the staminate flower 

 and the anthers rubbed over the pistil. The artificially pollin- 

 ated flower is protected from cross-pollination by placing a 

 rubber band around the petals. After a few days the petals of 

 the crossed flower abciss and at this time the stigma has turned 

 brown and is no longer receptive. This method was worked 

 out by John Bushnell, a graduate student in horticultural plant 

 breeding. From a total of 600 pollinations made under field 

 conditions in the summer of 1919, approximately 150 set fruit. 



Technic of Crossing. A thorough knowledge of flower struc- 

 ture of the species or variety to be worked with is essential before 

 crossing is undertaken. It is important to know which flowers 

 are the most vigorous and which set fruit the most freely. Many 

 varieties of wheat, for example, produce several seeds per spike- 

 let. The outer florets of the spikelets in the central part of the 

 rachis are more vigorous and usually produce larger seed. In 

 some Solanacece (for example, the petunia) the later flowers 

 form larger, healthier seed than those which first open (East, 



