E. V. Wulff —134— ffistorical Plant Geography 



It was, of course, a major error on the part of the first investigators 

 of the flora of Krakatau not to give adequate attention to such an im- 

 portant circumstance as the possibihty of seeds, roots, or stems having 

 been preserved in the soil. Although both Ernst and Docters van 

 Leeuwen consider that such parts of plants, due to the excessively 

 high temperature of the soil buried under the burning ashes of the 

 volcano, could not have been preserved, doubts as to their complete 

 destruction can always arise, as long as they were not eliminated at the 

 very first by special investigation. This is all the more true, since we 

 now have data of the preservation of seeds and the underground parts 

 of plants after eruptions of other volcanoes, e.g., after that of the vol- 

 cano Kamagatake, in southern Hokkaido (Japan). According to 

 JosHi (1932), at the time of the eruption of this volcano in 1929, which 

 lasted for two days, an area of 5,000 hectares on its slopes and at its foot 

 was buried under a layer of ashes and pumice, averaging one meter in 

 thickness and in some places as much as three meters thick. The 

 impenetrable forest that had previously covered its slopes was com- 

 pletely burned and destroyed by the products of the eruption. Joshi 

 for two years closely watched this area, and he found that there had 

 remained in the soil viable, though injured, underground parts of plants 

 that rapidly produced new shoots. Due to the irregularity of the relief, 

 the depth to which the soil was covered by ashes and pumice varied 

 and in some places was very inconsiderable. In such places as early as 

 two months after the eruption revegetation commenced, and after a 

 year had elapsed there appeared perennials that had developed from 

 underground parts that had survived. 



Nevertheless, there is no doubt that Backer's conclusion that a 

 study of the revegetation of Krakatau altogether lacks scientific interest 

 must be regarded as extreme. Even if part of the vegetation was re- 

 stored as a result of the preservation of seeds or underground parts of 

 plants, still a goodly proportion of the 324 species making up, accord- 

 ing to Docters van Leeuwen, the flora of Krakatau at the present 

 time were brought to the island by natural factors of dispersal. Kra- 

 katau constitutes an interesting case of the stocking of unoccupied 

 territory as a result of the transport of seeds over a relatively small 

 distance (ca. 25 miles) by sea currents, wind, and birds. 



Conclusions: — Plants are dispersed as result of the transport of tlteir 

 seeds by natural means only slowly and gradually, gaining new territory 

 step by step. The transport of seeds by such means over great distances 

 may be a factor in plant dispersal only in case the seeds encounter a 

 territory where ecological conditions are favorable for the given species 

 and where the original plant associations have been destroyed (which 

 otherwise would constitute an insuperable obstacle to the newcomer's 

 becoming established) or where there exist open formations, as, for in- 

 stance, on the seashore. Consequently, the transport of seeds by 

 wind, sea currents, birds, or other natural means cannot serve as an 

 explanation of discontinuous areas with widely separated parts. Nu- 

 merous facts, e.g., the occurrence of endemic species isolated from one 

 another on separate peaks of the same mountain chain, point to an 

 entirely different mode of origin of such areas. Hence, we must seek 

 an explanation of those moments in the geography of plants that are 



