E. V. Wulff — 128— Historical Plant Geography 



(1924) on the dissemination of the seeds of certain sedges. He found 

 that in the fruits of some species of the family Cyperaceae there exists a 

 special sponge -like tissue (the cells of which are filled with air) serving 

 as an aid in floating. About thirty species of this family were sub- 

 jected to study, and these were divided into the three following groups: 

 (i) those with fruits incapable of floating or capable of floating for a 

 very short time; (2) those with fruits capable of floating for a medium 

 length of time; and (3) those with fruits capable of floating for a pro- 

 longed period. It was found that the species with fruits entirely in- 

 capable of floating have the most extensive areas of distribution. 

 Here, it seems, there must be taken into consideration a number of 

 other factors, such as germination and taking root of seeds, adaptation 

 to new habitat conditions, etc., which it is impossible to gauge pre- 

 cisely. 



Moreover, those that are wont to take recourse in chance factors as 

 an explanation of all difiiculties encountered in understanding the 

 present-day distribution of plants do not take the trouble to ascertain 

 whether or not there exist the sea currents which, in their opinion, 

 carried the seeds to the necessary place and whether or not they pass 

 in the proper direction for such carriage, or to ascertain the time and 

 routes of flight of birds of passage, whether the beginning of flight 

 coincides with the ripening of the fruits and seeds of the plants under 

 consideration, whether the birds fly at such a time precisely to that 

 place where these seeds must be carried, or whether this period of 

 fruiting coincides with their flight in the opposite direction. 



Whenever alleged cases of the responsibihty of chance factors of 

 seed dispersal for the distribution of plants have been thoroughly in- 

 vestigated, they have been proved to have no foundation in fact. For 

 example, we may take the critical analysis which Staff (1894) made 

 of the species in the flora of Mt. Kinabalu (Borneo). The flora of this 

 mountain is composed of species growing Hkewise not only on other 

 islands of the Indian Ocean as far away as New Guinea but also in the 

 Himalayas. As a result of this analysis, Staff came to the conclusion 

 that neither birds nor present-day physiographic factors can serve to 

 explain the combination of species growing on Mt. Kinabalu. He 

 found that the higher the altitude, i.e., the more untouched by man 

 the vegetation, the greater the number of endemics, and that there 

 was no correlation whatsoever between the number of endemics and the 

 possibilities for dispersal due to the possession of special adaptations. 

 It would seem that where there was a greater number of plants having 

 such adaptations for dispersal, there should have been fewer endemics, 

 but in many cases the reverse was true. 



It was formerly supposed that the lower, spore-bearing plants, 

 whose spores are so easily dispersed by the wind, must have an ex- 

 ceptionally extensive geographical distribution. However, the more 

 their habitats have been subjected to study, the more it has been found 

 that such plants are localized in definite areas, their distribution paral- 

 leling that of the flowering plants. Similarly, if the chance transport of 

 seeds over great distances was of such decisive significance, this should 

 be particularly reflected in the distribution of aquatic plants, especi- 

 ally of angiosperms living in the ocean or in large bodies of fresh water. 



