228 



GENERAL BIOLOGY 



FIG. 82. Mendelian inheritance in nettles : I, the leaves of the two 

 parents, Urtica pilulifera (at the left) and Urtica dodartii (at the right) ; 

 the serrated type of leaf is dominant ; II, the leaves of the hybrid's 

 offspring (F2 generation) ; the pure gametes are represented by the black 

 and white disks, and the "impure" by the cross-barred disks ; in ///, the 

 Fa generation, their descendants are constant (right and left), the other 

 two fourths sorting out as before. (From Hertwig, after Strassburger.) 



