660 Mutations • 



that govern the production of anomalies, and 

 we may assume them to lie within reach of our 

 experiments. The experimental treatment of 

 the origin of species may also be looked upon as 

 a method within our grasp. 



The validity and the significance of these 

 considerations will at once become clear, if we 

 choose a definite example. The broadest and 

 most convincing one appears to me to be af- 

 forded by the cohesion of the petals in gamo- 

 petalous flowers. According to the current 

 views the families with the petals of their 

 flowers united are regarded as one or two main 

 branches of the whole pedigree of the vege- 

 table kingdom. Eiehler and others assume 

 them to constitute one branch, and therefore one 

 large subdivision of the system. Bessey, on the 

 other hand, has shown the probability of a sep- 

 arate origin for those groups which have in- 

 ferior ovaries. Apart from such divergencies 

 the connation of the petals is universally recog- 

 nized as one of the most important systematic 

 characters. 



How may this character have originated? 

 The heath-family or the Ericaceae and their 

 nearest allies are usually considered to be the 

 lowest of the gamopetalous plants. In them the 

 cohesion of the petals is still subject to rever- 

 sionary exceptions. Such cases of atavism may 



