SECT. II 



PHYSIOLOGY 



287 



that the liybrid exhibits au intermediate character. More usually the hybrids 

 completely resemble in this respect either the paternal or maternal parent, the 

 character of the one parent being dominant in the hybrid while the other remains 

 latent (Law of dominant characters). This is the case for example in hybrids 



Fig. 220. — Hybridisation of Urtica piluUfera (to the left, above) witli U. Dodarti (to tlie right). 

 I, First generation which, tliough hybrid, shows the dominant leaf-form of U. inlulifera. Its 

 .sexual cells, in which a separation of the chaiacter occurs, give rise in generation II to a pure 

 and constant piluUfera, a pure Dodarti, and two hybrids. In generation III the pure forms to 

 the right and left are constant, the hybrids in the centra show further splitting of characters. 



between Urtica piluUfera with serrate leaves and U. Dodarti (Fig. 220). The 

 hybrids have all serrate leaves like U. inlulifera, so that in the second generation 

 the proportion of serrate-leaved to entire-leaved individuals is per cent 75 : 25 

 (3 : 1). Only 50% of the serrate-leaved individuals are, however, of hybrid nature 

 and continue to show a similar 'plitting of characters in the next generation ; 

 25% have become pure U. piluUfera. It is impossible to predict which characters 



