MODE OF REPRODUCTION IN RELATION TO BREEDING 41 



hybrid plants were obtained and from the M. sativa seed about 

 7.5 per cent. A part of the difference in the results is doubtless 

 due to the fact that the plants produce a smaller number of 

 flowers and are procumbent to prostrate in habit. To find the 

 amount of cross-pollination that normally occurs in alfalfa, one 

 might average the above results and multiply the result by two. 

 This gives in the neighborhood of 50 per cent, of natural crossing 

 which is only indicative of the probable amount. 



Grasses. Some studies with grasses have been reported by 

 Frandsen (1917). Results obtained are given in the following 

 table. Some sterility is indicated by comparing the results of 

 self-fertilization with those of cross-fertilization and natural 

 pollination. Poa fertilis and Bromus arvensis appear self-fertile. 

 Considerable self-sterility is indicated in orchard grass, timothy, 

 and fescue. 



TABLE III. POLLINATION OF GRASSES 



EFFECTS OF A CROSS IN NORMALLY SELF -FERTILIZED SPECIES 



A cross between closely related varieties frequently exhibits a 

 quite marked increase in vigor when compared with the parents. 

 This is a manifestation of the same phenomenon as decrease in 

 vigor which is commonly the result of self -fertilizing a naturally 

 cross-fertilized species. With self -fertilized crops it is usually 

 not possible to utilize this increased vigor because the cost of 

 producing crossed seed is too great. Examples of FI crosses in 

 tomato, tobacco, and wheat will be given. 



Table IV gives the comparative yields of first generation 



