530 



EVOLUTION 



The mutations involved various kinds of characters. One of 

 the new forms, Oenothera brevistylis, had, among other distinc- 

 tive characters, a much shorter style than the Oenothera La- 

 marckiana. Another new form, Oenothera laevifolia, had smooth 

 leaves and much prettier foliage than the parent type, and its 

 petals were not notched. One of the finest and rarest of the 

 mutants was the Oenothera gigas (Fig. IflS), which was stronger, 

 bigger, and more heavily built than the parent. Others of the 

 ' new forms differed from 



the parent in other char- 

 acters. 



As to what a new form 

 is, can be determined only 

 by breeding it and its 

 parents in pedigree cul- 

 tures. A new form may 

 result from crossing be- 

 tween two parents with 

 different characters and, 

 therefore, be a hybrid. 

 The new form may be 

 due to the fact that the 

 parent is a hybrid or de- 

 scendant of a hybrid and 

 consequently does not 

 breed true, thus producing 

 offspring different from 

 the parent type. If the 

 parents are pure, and the 

 new form is not a hybrid, 

 it must be a mutant or a 

 fluctuating variant. If it breeds true, it is a mutant; other- 

 wise, it is a fluctuating variant. 



By growing the parents of the new forms in pedigree cultures 

 for a number of generations, he found that they bred true, 

 except for the new forms which occasionally appeared, and 

 concluded that the parents were pure. Since the parents of 

 the new forms were carefully pollinated artificially, so as to 

 prevent crossing between parents differing in characters, the new 

 forms were not the result of hybridizing. They were either 



FIG. 473. The Giant Evening Prim- 

 rose (Oenothera gigas}, one of the mutants 

 from Lamarck's Evening Primrose. After 

 De Vries. 



