520 VAEIATIONS 



bearing seeds largest on the average for the parents of the next 

 generation. He continued this for a number of generations, but 

 obtained no increase in the average size of the seeds when all 

 individuals of each generation were considered. Similar results 

 have been obtained by other investigators in attempting to 

 intensify certain desirable variations in Wheat, Oats, and in pure 

 lines of other plants. For example, an effort to increase the yield 

 in a strain of Oats by selecting each year the best yielding plants 

 for seed gave practically no increase in yield after a number of 

 years of selection. 



Mutations. — Mutations are leaps in variations that commonly 

 result in the origin of new forms of organisms,,: Between the old 

 forms and the new there are no transitional forms, but the varia- 

 tions are such that the new forms arise at one bound, and are 

 often so different from previous forms as to be classed as new 

 varieties or species. Since mutations are not characterized by 

 transitional stages, they are commonly called discontinuous 

 variations, in contrast to fluctuating variations which show 

 various degrees of magnitude. Mutations also differ from most 

 fluctuating variations in that they are commonly transmitted to 

 offspring and thus are perpetuated in future generations. Since 

 mutations are wide departures in variations and commonly 

 breed true, they establish new standards or modes. This can be 

 illustrated in case of Beans. Dwarf or Bush Lima Beans ranging 

 in height around 20 inches have originated by mutations from 

 Pole Lima Beans which commonly range in height from 3 to 5 

 feet. In both cases the height fluctuates, being different in differ- 

 ent individuals in the same generation and also in different genera- 

 tions, but the most usual height or mode around which height 

 fluctuates is very different in the two varieties. The mode is 

 probably less than 20 inches for the Bush Lima Beans and 

 probably more than 40 inches for the Pole Lima Beans. It is 

 obvious in this case that the mutation has resulted in a very 

 pronounced reduction in height, resulting in a very different 

 center around which height fluctuates. Without any inter- 

 mediate stages or suggestion of their appearance, these new forms 

 with characters fully established come forth among the offspring 

 of Pole Lima Beans. They breed true and thus are entitled to 

 be called a new variety. Professor Hayes of the Connecticut 

 Agricultural College has called attention to mutations in Tobacco. 



