54 



Plant-Breeding 



ment in which the plant lives. The mutations arise from 

 causes yet unknown, although these causes are considered 

 to be physiological. Probably many so-called mutations 

 are hybrids and hence not mutations in the strictest 

 sense. 



Differences between fluctuating variations and mutations : 



1. Fluctuating variations are very common and are 

 to be found in all plants and animals. Mutations occur 

 intermediately and are rare. 



2. Fluctuating variations are thought not to be trans- 



mitted. Muta- 

 tions are trans- 

 mitted. 



3. Fluctuating 

 variations pre- 

 sent a series of 

 differences which 

 may be plotted 

 on a frequency 

 curve and obey 

 the laws of 

 chance. Muta- 

 tions or saltatory 

 variations do not 

 obey the laws of 

 chance, and can- 

 not be plotted in 

 the form of a 

 frequency curve. 



4. Fluctuating variations do not lead to a new perma- 

 nent mean of the race. Mutations cause a new mean to be 



its Its 13 OS 



16 16.5 17 125 



FIG. 10. Variations in the amount 

 in 40,000 beets. 



of sugar 



