Mutations 183 



was markedly different from the parental type was looked 

 upon as a freak and was called by breeders a *' sport." Dar- 

 win knew of the existence of these sports and indeed 

 described some in his books. He did not, however, take them 

 seriously as possible sources of new breeds or species. 



In 1886 Hugo de Vries gathered the seeds from some 

 evening primroses which were growing in vacant lots. These 

 had apparently escaped from cultivation in Dutch gardens, 

 since the plants are natives of North America. From these 

 seeds he obtained over 1 5 ,000 new plants, among which were 

 five extremely small individuals and five others with ex- 

 tremely broad leaves (Fig. 48). These two varieties differed 

 not only from each other and from the parent plants that 

 supplied the seeds but also from other known varieties of the 

 genus. These two sports were cultivated separately, but iden- 

 tical forms appeared spontaneously in successive generations 

 grown from the seeds of the parent type. Ten years later, 

 and after four generations of seeds had been grown from the 

 original stock, there appeared seven new varieties including 

 the dwarf and the broad-leaf of the first experiments. These 

 new types showed very distinct characteristics such as ob- 

 long leaves, reddish veins, pale flowers, gigantic stalk, and so 

 on. It was possible by means of careful breeding to preserve 

 new qualities and eventually to recombine one with another 

 and with the contrasting characters of the parent type in 

 accordance with the so-called Mendelian principles of 

 heredity. In the thirty years that have elapsed mutations 

 have been observed in many plants and animals, both wild 

 and domestic. 



The most intensive studies of the principles of genetics 

 have been carried on in the Biological Laboratory at Colum- 

 bia University under Professor Thomas H. Morgan, now at 

 the California Institute of Technology. His work with the 

 fruit fly Drosophila revealed literally hundreds of details 

 wherein this comparatively simple organism may differ as 

 between one individual and another. A very large number 

 of these departures from the type were mutations in the 

 sense that they had a definite hereditary basis. Inasmuch as 



