126 Outline of Genetics 



white plastids at play to account for the green and white areas; 

 that it must be rather a matter of the ''general physiological 

 condition " of the two types of tissue. It is interesting to note that 

 in this case a type of somatic segregation occurs on the ear of the 

 variegated plant, resulting in certain groups of seeds that will 

 produce green seedlings, other groups of seeds that will produce 

 white seedlings, and still other groups of seeds that will produce 

 variegated seedlings. 



In short, the cases of chlorophyll inheritance on a non-Men- 

 delian basis are still under considerable discussion; a perfectly 

 clear interpretation of the phenomena is not as yet available. Of 

 this much, however, we may be sure: there is such a thing as non- 

 Mendelian inheritance, and it becomes manifest in connection 

 with a type of character which, on other occasions, is inherited 

 according to the normal Mendelian scheme. In any event, such 

 cases should not be regarded as a violation of Mendel's law, but 

 merely as something outside the scope of Mendel's law, since they 

 are evidently transmitted by some extra-nuclear mechanism. 



In good part the known examples of non-Mendelian inherit- 

 ance are limited to such cases of chlorophyll inheritance as have 

 been cited above. There is another small group of cases, however, 

 that must also be regarded as illustrating non-Mendelian inherit- 

 ance, although in quite a different way. Bateson and his 

 coworkers (4) have discovered certain instances (e.g., inheritance 

 of doubleness in Matthiola) in which the male and female organs 

 of the same plant differ in the factors they carry. A clear explana- 

 tion of this phenomenon has not been provided, but whatever 

 the explanation may turn out to be, it seems certain that it will 

 provide an exception to the normal Mendelian mechanism. Such 

 cases have led Bateson to suspect that plants, as genetic machines, 

 differ fundamentally from animals, segregation being clearly 

 connected with synapsis in animals but not always in plants. 

 This difference in the machinery may be tied up with the fact that 

 "in animals the rudiments of the gametes are often visibly sepa- 

 rated at an early embryonic stage, whereas in the plant they are 

 given off from persistent growing points." 



