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CHAPTER III 



(a) Nowhere is there such a congregation of migrating birds, particularly of 

 swimmers and waders, as on the shores of lakes and of the sea. 



(b) Small objects of any kind attach themselves most easily to the feet and feather 

 of a bird in water or on very wet places, especially together with mud. After the 

 bird has taken wing, the mud dries up quickly and remains well fixed. 



(c) Ubiquistic freshwater organisms, by means of their usually much wider 

 geographical distribution in comparison with terrestrial ones, and at the same time 

 their confinement to a more disjunct mosaic of suitable habitats, often of a tem- 

 porary character, apparently are much better adapted to passive dispersal than 

 terrestrial organisms are. Among the methods exploited, transport with birds 

 should not be underestimated {vide the extract by Thienemann, 1950, p. 156- 

 158). 



(d) A special case is provided by Potamogeton epihydrus. The fruits of Pota- 

 mogeton are a normal part of the food of swimming birds, especially of ducks, 

 and Lohammar (1954) has shown that the passage through a bird's intestines 

 highly favours the germination. 



To my mind, the theory of bird-transport should be earnestly considered in the 

 case of four of the "American" plants: Eriocaulon septangulare, Limosella subulata, 

 Myriophyllum alterniflorum americanum, and Potamogeton epihydrus; in addition, 

 for the single animal of this geographical group, Heteromeyenia ryderi. 



It may sound absurd that causal appearances of wind-driven birds should have 

 proved more efficient as an agency enlarging the area of transported organisms 

 than birds on their normal route of migration. This is, however, a seeming dis- 

 crepancy only. Dispersal of seeds, fresh- water animals, &c., along the great 

 highways of migrating birds has gone on regularly for thousands of years and re- 

 sulted in continuous species' areas, regarded by us as "natural". Yet the erratic 

 east-west dispersal is predestined to give a better effect proportionally, because it 

 usually means the removal into a place with a climate similar to that of the starting- 

 point. 



The two remaining plants must be treated separately. They are less hygrophilous, 

 neither of them is a w-ater or even a shore plant, and their diaspores are different. 

 Spiranthes romatizoffiana is an Orchid with very numerous and very minute seeds 

 which are wind-spread and must be assumed to constitute a regular component 

 of aerial plankton. The resistance of the seeds to cold and exsiccation should be 

 investigated experimentally. Probably the distribution of the species is more 

 restricted by the limited possibility of the seedling finding the right fungus for 

 mycorrhiza than by powers of dispersal. 



It is difficult to understand that the globular seeds of Sisyrinchium could be suited 

 for passive transport of any kind or that any vegetative part of the plant could 



