Diskussion zum Vortrag Crampton. 647 



valley into six neighboring areas in which it has produced new 

 and characteristic varieties. P. clara occurred thirty years ago 

 in only twelve Valleys of the Southern quadrant of Tahiti; it is 

 now found in fifteen additional Valleys and as noted above in 

 some of these new regions as well as in certain of its former habi- 

 tats it has produced new types. Some of the varieties of P. ota- 

 heitana such as sinistrorsa exhibit precisely similar changes. From 

 these and similar facts we may gain some idea of the rapidity of 

 organic differentiation in nature. 



It is implied in the foregoing although not expressly stated 

 that the production of new varieties occurs through mutation. 

 That a new form thus produced is actually a mutant in heredity 

 as well as in appearance is clearly demonstrated by the facts of 

 inheritance in numerous cases discovered in different islands of 

 the Society group. 



The causes for organic differentiation cannot be found in 

 environmental circumstances. The latter are more uniform in 

 tropical islands like those under consideration than anywhere 

 eise in the world. It is difficult to see how external conditions 

 could bring about the establishment of dextral varieties of a 

 species on one side of a mountain ridge and sinistral varieties 

 on the opposite side of the same ridge; these relations actually 

 appear in at least four cases in Tahiti. Furthermore a new variety 

 may appear as a mutant in an old portion of the ränge of a species 

 or it may appear with equal readiness in some part of the recently 

 invated territory. Finally Jordan's Law holds true for 

 later and not for the early stages in the differentiation of an ori- 

 ginal type into its subordinate forms. At the outset the new 

 variety necessarily occurs in the region of its parental form. 



Diskussion: 



Herr Dr. E. Hartert (Tring) fragt, was für Beweise vor- 

 lägen, daß das Vorkommen von Arten im Jahre 1861 so be- 

 schränkt war, wie der Redner annahm, oder ob es nicht möglich 

 sei, daß hier Beobachtungsfehler vorlagen, da in früheren Zeiten 

 selten so intensiv und lokal gesammelt wurde wie heutzutage. 



Ferner ob eine „ Mutation" wirklich beobachtet wurde oder 

 ob nur aus den Beobachtungen des Forschers darauf geschlossen 

 wurde. 



Herr Prof. Dr. H. E. Crampton: The answer to the 

 first question was as follows: a thorough exploration of Tahiti 

 and other islands was made by G a r r e 1 1 prior to his death 

 in 1889. By comparing the present distribution of species of 

 Partula with their former locations, the evidence of migration 

 and formation of new varieties is obtained. 



