No. 509] THE CATEGORIES OF VARIATION 277 



late as around a new center of equilibrium. Weismann 

 postulates a self-regulating power in the germ plasm 

 which keeps numerous minor fluctuating variations from 

 producing any essential modification of the stock. If, 

 however, a certain variation forms a new center of stabil- 

 ity it may be permanent. The various mutants of (Eno- 

 thera lamarckiana, 2 most if not all of which contain the 

 potency of giving rise to any of the others and which pre- 

 sent very different degrees of stability, may be due to 

 more or less stable forms which the germ plasm may as- 

 sume rather than the creation of new kinds of germinal 

 units. The stability of a variation may be due, however, 

 not so much to its extent as the analogy with the polyhe- 

 dron might lead us to expect as to its kind. Variations 

 which are physiologically congruent with the organized 

 structure of the germ plasm form stable races; those 

 which are not tend to become reduced sooner or later to 

 the norm through the regulatory activity of this sub- 

 stance. 



The germ plasm may be conceived to exercise, in regard 

 to its variations, a kind of selective activity which may 

 manifest itself as a proneness of the organism to vary 

 along certain lines. It is well known that there are partic- 

 ular types of variation which crop out independently and 

 moe or less frequently and may be faithfully perpetu- 

 ated. Polydactylism, split-hand and split-foot, albinism 

 and melanism, the appearance of races of hairless animals 

 and glabrous plants, the development of nectarines from 

 peaches and peaches from nectarines, the origin of peloric 

 flowers, etc., have occurred many times in independent 



2 It is of course possible that the mutations of (Enothera Lamarckiana 

 result from the impurity of the stock. The species has been for a long 

 time cultivated as an ornamental flower, and we have nothing but conjecture 

 regarding its origin. Should it turn out to be derived from a mixture of 

 two or more forms the mutation theory would be deprived of some of its 

 best evidence, but there would still remain a considerable number of muta- 

 tions from pure ancestry. In (Enothera gigas the interesting fact has 

 been discovered that there is double the normal number of chromosomes. 

 Whether this is the cause or the effect or merely one instance of the dif- 

 ferences between this mutant and the type is unknown. 



