326 Plant-Breeding 



Factor hypothesis. An assumption that organisms may 

 contain various hereditary units which do not appear in their 

 body cells. This is especially applied to color units. Very 

 often these factors do not appear until the plant has been crossed 

 with another plant containing a complementary factor. 



Fi. A symbol introduced by Bateson, to designate the 

 first filial or hybrid generation. 



F 2 . A symbol for the second generation. 



F 3 . A symbol for the third hybrid generation. And so on. 



Galton curve. A curve, devised by Galton, when the values 

 for all the individuals are recorded consecutively in an ascending 

 series. The class values are plotted on the vertical axis. 



Gamete. A mature sex- or germ-cell , which will produce a 

 new individual upon uniting with another such cell of the op- 

 posite sex. 



Genetics. A study of the phenomena of variability and 

 heredity, or of the physiology of descent, as affecting individuals 

 or races of plants, animals, or human beings. 



Genotype. A type represented by individuals of the same 

 germinal constitution. The' nature of such a type can be 

 determined only by a breeding test, not by inspection. 



Heterozygote. An individual formed by the union of two 

 germ-cells of unlike constitution. 



Homozygote. An individual which is of a pure type in regard 

 to a certain character because both of its parents were of the 

 same gametic constitution. 



Hybrids. The offspring of crosses between individuals of 

 distinctly different natures. 



Hypostatic. Used to describe a color factor which is con- 

 cealed by higher color factors. (See Epistatic.) 



Mutation. A sudden variation, differing from its parents 

 in a distinct character or characters, and able to transmit its 

 new characters in full degree to its offspring. 



Nulliplex. A condition of an individual when it does not 



