174 HEREDITY AND EVOLUTION IN PLANTS 



A third type of distribution is that of limited range, 

 such as has been mentioned above for the venus's fly- 

 trap and the giant redwood trees. Among genera thus 

 distributed are Wiesnerella Javanica Schiff., known at 

 present only from Mt. Gedeh, in Java, and Geothallus 

 tuberosus Campbell, known only from near San Diego, 

 California. These ranges may ultimately be extended, as 

 was that of Treubia insignis, known for a time only from 

 Mt. Gedeh, but later found by its original discoverer 

 in New Zealand. 



As already noted, in order to become widely distributed, 

 either continuously or discontinuously, a plant must either 



1. Have reproductive bodies capable of rapid distribu- 

 tion over wide areas, or 



2. Possess sufficient antiquity to have been in process 

 of dissemination for a comparatively long period of time. 

 In the former case, its reproductive bodies must be of such 

 nature as to resist unfavorable environment and vicissi- 

 tudes, during transit over long distances, and be able to 

 establish themselves readily in the new habitat, especially 

 in competition with the plants already established, and pos- 

 sibly also in an unfavorable environment. Now the spores 

 of many of the most widely distributed Hepaticce are not 

 of this nature. We can hardly explain the present distribu- 

 tion of such widespread tropical genera as Dendroceros, 

 Monoclea, and Dumortiera, says Campbell, by the theory 

 that their spores could be carried across the wide ocean 

 barriers that separate the regions where they now occur, 

 as the spores are not of the type that could be carried long 

 distances without perishing. Since there are no connecting 

 forms in the higher latitudes that could explain the passage 

 of these forms from one tropical zone to the other, we can 



