122 MENDELISM CHAP. 



That the possibility of a difference between the ovules 

 and pollen grains of the same individual must be taken 

 into account in future work there is evidence from quite 

 a different source. The double stock is an old horti- 

 cultural favourite, and for centuries it has been known 

 that of itself it sets no seed, but must be raised from 

 special strains of the single variety. "You must under- 

 stand withall," wrote John Parkinson of his gilloflowers, 1 

 "that those plants that beare double flowers, doe beare 

 no seed at all ... but the onely way to have double 

 flowers any yeare is to save the seedes of those plants of 

 this kinde that beare single flowers, for from that seede 

 will rise some that will beare single, and some double 

 flowers." With regard to the nature of these double- 

 throwing strains of singles, Miss Saunders has recently 

 brought out some interesting facts. She crossed the 

 double- thro wing singles with pure singles belonging to 

 strains in which doubles never occur. The cross was 

 made both ways, and in both cases all the FI plants were 

 single. A distinction, however, appeared when a further 

 generation was raised from the FI plants. All the FI 

 plants from the pollen of the double-throwing single be- 

 haved like double-throwing singles, but of the FI plants 

 from the ovules of the double throwers some behaved 

 as double throwers, and some as pure singles. We are 

 led to infer, therefore, that the ovules and pollen grains 



1 Paradisus Terrestris, London, 1629, p. 261. 



