628 PRACTICAL PROBLEMS 



of crossing is, therefore, best adapted to plants, which can be 

 propagated asexually, and therefore free from the limitations 

 just mentioned. 



SPECIAL EXERCISES 



Make calculations showing the relative expense of grading as compared 

 with breeding pure for different classes of animals. 



Also make critical study of many pedigrees of famous animals in order 

 to trace the systems of breeding actually employed, especially as to line 

 breeding and inbreeding. 



ADDITIONAL REFERENCES 



Loss OF VIGOR FROM INBREEDING. By H. J. Webber. Science, 1901, 



No. 320, p. 257. 

 POLLINATION OF APPLES AND PEAS. Experiment Station Record, 



XIII, 620. 

 RECIPROCAL CROSSES (with extended bibliography). Maine Station 



Report, 1904, pp. 81-89. 





