558 STRUCTURE AND LIFE HISTORIES 



where a and h each equal i. In the plants the multi- 

 plication of inheritances (produced in fertilization) was 

 as follows: 



eggs {s + 7C') X sperms {s + ^^0 = ^^ + 2sw -\- ww 



where w = wrinkling and s = absence of wrinkling, i.e., 

 smoothness. 



479. Theory of Purity of Gametes. — The above ratio 

 is what we would expect if half of the egg-cells and half 

 of the sperm-cells in a heterozygous plant (one of the Fi 

 generation), carried only character-units or determiners^ 

 that make for smoothness; the other half only those 

 factors that make for wrinkling, giving 5 and w egg-cells, 

 and s and w sperm-cells in equal numbers. Therefore, in 

 pollination the chances would be equal that an s-egg would 

 be fertilized with either an 5-sperm or a w-sperm, giving 

 {s -\- w) X {s -\- w) = ss -{- 2SW -\- WW. Since s is dominant 

 over w the product should be written: 



ss -j- siii") + s{w) -\- ivw 



giving in external appearances 35 + iw. Since the re- 

 sult actually observed is what it would be ij the gametes 

 were thus ''pure" for smoothness and wrinkling, Mendel 

 concluded that they really are, and moreover that each 

 character behaves as a unit, appearing and disappearing 

 in its entirety. 



480. Character -units versus Unit-characters. — As just 

 stated, Mendel held that the various visible characters of 

 his plants (dwarfness, for example) behaved as units, 



^ The substance or condition (protoplasmic constitution), whatever it is, 

 in the germ-cells that corresponds to any given character of the plant is 

 variously referred to by the terms factor, determiner , gene (= producer), 

 character-unit, and others. These terms are essentially synonyms. 



