SCOPE OF GENETICS 23 



of several factors to produce them. Never- 

 theless though the character only appears 

 when all the complementary ingredients are 

 together present, each of these severally and 

 independently follows, as regards its trans- 

 mission, the simple rules I have described. 

 This complementary action may be illus- 

 trated by some curious results that Mr 

 Punnett and I have encountered when ex- 

 perimenting with the height of Sweet Peas. 

 There are two dwarf varieties, one the 

 prostrate "Cupid," the other the half-dwarf 

 or "Bush" Sweet Peas. Crossed together 

 they give a cross-bred of full height. There 

 is thus some element in the Cupid which 

 when it meets the complementary element 

 from the Bush, produces the characteristic 

 length of the ordinary Sweet Pea. We may 

 note in passing that such a fact demonstrates 

 at once the nature of Variation and Rever- 



