Mutations and Heredity 379 



ing the flowers and fruit. The new forms differed not only 

 in many details of the tall stem and flowers and leaves, 

 but also in many details of the rosette. That is to say, 

 the step from the parental form to the new form was one 

 of coordinated characters, affecting all the organs (and 

 functions or processes) of the species, not merely one or a 

 few traits. 



De Vries continued his observations and experiments 

 nearly twenty years before he announced his new theory of 

 species formation, the mutation theory. His experiments in- 

 cluded, incidentally, the independent rediscovery of Mendel's 

 principles of heredity (see pages 287 f ) . The mutation the- 

 ory starts out with the first reliable facts of inheritance that 

 we have managed to capture — the so-called laws of Mendel. 

 It goes farther, however, in asserting that the beginning of 

 a new species is to be found in particular individuals, who 

 start out upon life with a distinct break in the continuity 

 of the germinal material. These new individuals have in- 

 herited something from their parents, but somewhere in the 

 chain of events something was added, or something was 

 taken away, with the result that the further heritage is 

 modified. 



The mutation theory meets the logic of Lamarck's the- 

 ory, but locates the critical point at which change emerges in 

 another part of the chain. It is not the modified individual 

 that influences the germinal plasm which he transmits. 

 Something happens to the germinal material directly — 

 either through some agency acting from without (for ex- 

 ample, a chemical influence. X-rays, temperature) or through 

 some irregularity in the behavior of the chromosomal pro- 

 toplasm itself (as in non-disjunction, cross-over, new fac- 

 torial combinations, and so on) . Some of these departures 

 from the conventional types will reproduce themselves in a 

 new line. If they can meet the conditions of life, they will 

 establish a new race, type, species — otherwise they will 

 perish, as any unadapted unit. 



