MUTATION. 167 



about "Generatio spontanea" in the time of Pasteur. Believ- 

 ers in this process urged that this spontaneous creation could 

 not possibly have anything to do with the preparation of the 

 test-tubes filled with food-media. It seemed obvious, that if a 

 spontaneous growth of bacteria is possible on potatoe, it mat- 

 ters not at all whether this potatoe is raw or boiled. In the 

 same way, we hear the statement nowadays, that if spontaneous 

 geno- variation, the spontaneous loss of a gene is possible, it can 

 happen as well in a family of plants or animals which are not 

 strictly pure for their genes, as in a family in which all mem- 

 bers are strictly homozygous. The difference comes in from the 

 side of the necessity of control. Pasteur reasoned, that if 

 bacteria were spontaneously created, they could be created on 

 boiled as well as on raw potatoe, and the fact that spontaneous 

 growth was never observed on well sterilized media was very 

 significant. 



Some authors still believe in the possibility of demonstrating 

 spontaneous geno- variation in impure material, and without 

 control-matings. One example is the so-called spontaneous pro- 

 duction of a dwarf of Oenothera biennis by Stomps, a pupil of 

 de Vries. This author crossed strains of 0. biennis which differ- 

 ed in shape of the flowers. One family had extremely narrow 

 petals, but otherwise the two were pheno-typically alike. In 

 the second hybrid generation Stomps obtained two novelties, 

 a giant and a dwarf, which he calls-mutations. Of course such 

 an instance is an extreme case of abuse of the term. Very few 

 authors nowadays would call the production of novelties in 

 the second generation of a cross mutation, at least not in the 

 sense of real spontaneous geno-variation, in de Vries' sense of 

 the word. It is obvious, however that, if the two parents had not 

 been different in flower shape, if they had been identical pheno- 

 typically, the case would have looked much more like a real 

 mutation. 



In fact, Stomps obtained the same dwarf forms from pure- 

 bred Oenotheras, in what he calls a "pure line" of Oenothera. 

 That is to say, wild-growing plants, inbred for four generations, 



