74 BREEDING CROP PLANTS 



flowers which had just opened, no pollen remained. Small 

 pieces of blotting paper were used to remove excess moisture and 

 then pollen was applied. Fifteen flowers of lettuce were first 

 crossed by this means and some seed was produced in each 

 flower. The lettuce flowers and those of other closely related 

 Composite close soon after pollination. 



Certain small rubber-bulb syringes have been found satis- 

 factory for field work. These are used to depollinate the flowers 

 with water. .For a complete description of artificial cross- 

 pollination of alfalfa flowers the reader is referred to Oliver. In 

 the flower to be used as the female, the anthers have already 

 dehisced but can not perform the act of fertilization until the 

 flower is 1 ripped. To trip the flower and secure as small a per- 

 centage of pollination as possible is the aim. The technic of 

 tripping and depollinating as well as the technic of crossing is a 

 matter of practice. Oliver records that more than two-thirds of 

 the alfalfa pollinations were successful by this method. 



Summary of Technic of Crossing. Some important features 

 of the technic of crossing may be summarized. 



1. Make a careful study of the structure of the flower before 

 commencing operations. This may be done with the aid of a 

 dissecting microscope. 



2. Determine which flowers produce the larger, healthier seeds 

 and which set seeds the more freely. 



3. Learn the normal method of blooming of the flower, the 

 period of receptivity of the pistil, and the length of time the 

 pollen grains are capable of functioning. 



4. Procure the necessary tools and see that these are of an 

 efficient kind for the work to be undertaken. 



5. Be careful not to injure the flowering parts any more 

 than is necessary. Do not remove the surrounding flower parts, 

 i.e., petals in flowering plants, glumes of grasses, etc. unless 

 necessary. 



6. A few crosses well made are of much greater value than 

 many pollinations carelessly executed. 



