Lectuee X 



MENDEL 'S LAW OF BISEXUAL CROSSES 



In the scientific study of the result of crosses, 

 the most essential point is the distinction of the 

 several characters of the parents in their combi- 

 nation in the hybrids and their offspring. 

 From a theoretical point of view it would be 

 best to choose parents which would differ only 

 in a single point. The behavior of the differen- 

 tiating character might then easily be seen. 



Unfortunately, such simple cases do not read- 

 ily occur. Most species, and even many ele- 

 mentary species are distinguished by more than 

 one quality. Varieties deviating only in one 

 unit-character from the species, are more com- 

 mon. But a closer inspection often reveals 

 some secondary characters which may be over- 

 looked in comparative or descriptive studies, 

 but which reassume their importance in experi- 

 mental crossings. 



In a former lecture we have dealt with the 

 qualities which must be considered as being due 

 to the acquisition of new characters. If we 



276 



