IMPORTANCE OP MUTATIONS RECOGNIZED 



525 



Among the many thousand plants grown in the experimental 

 garden a number of new forms appeared. Some of the new forms 

 appeared only once and some appeared in a number of genera- 

 tions. The new forms differed in various ways from each other 

 and from the parent type. One new form, called Oenothera 

 nanella, was a dwarf; another form, called Oenothera gigas, 

 {Fig. 473) was more robust and its leaves were broader than the 

 parent type. One new form, called Oenothera rubrinervis, was 

 chiefly characterized by much red pigment in its epidermis. The 

 new forms were self-fertilized 

 through a number of genera- 

 tions to test their purity. A 

 number of them bred true to 

 the new type and were con- 

 sidered capable of maintaining 

 themselves true to the new type 

 if allowed to grow wild. Thus 

 De Vries had actually seen new 

 species arise in his experimental 

 cultures by the process of mu- 

 tation and he was convinced 

 that mutations have an impor- 

 tant place in the origin of new 

 species. In 1901, after spending 

 20 years in experimental work 

 on this problem, he pubUshed 

 his "Mutation Theory" in 

 which he sets forth the idea 

 that new types or species arise 

 through mutations and not by 

 means of fluctuating variations 

 as was previously supposed. In 

 demonstrating the importance 



of the pedigree method of study and in the accumulation of evi- 

 dence supporting the mutation theory, De Vries has made a con- 

 tribution of inestimable value to the study of variations. 



Cause of variations. - The plant and animal breeders are as 

 much concerned about the causes as about the kinds of variations, 

 for in order to control variations their causes must be controlled^ 

 Variations are the means by which better types of plants and 



Fig. 473. — The Giant Evening 

 Primrose {Oenothera gigas), one of the 

 mutants from Lamarck's Evening 

 Primrose. After De Vries. 



