420 



PLANTS, SEEDS, AND CURRENTS 



Western Europe and the Azores. Sibthorpia holds a similar number 

 of species which live in the Andes, in the mountains of Mexico, in 

 Europe, in Africa, and in Nepaul. The Canary group has its own 

 species, and Sibthorpia europcea not only extends to the Azores, 

 but is found in the mountains of the Cameroons and in the Abyssinian 

 Alps. 



3. The Modes of Dispersal of the Aquatic and Subaquatic Plants. — 

 It may be observed that in most cases these Azorean plants possess 

 minute seeds or very small seed-like fruits, such as we find in Peplis 

 portula, Littorella lacustris, Callitriche aquatica, and Scirpus fluitans, 

 which could have been transported to the group in mud adhering 

 to birds. The small fruits of the common Potamogeton (P. poly- 

 gonifolius) are 2-3 mm. in size and float in quantities on the surface 

 of the ponds and lakes in the latter part of the summer. They 

 would be readily swallowed by wild ducks and other waterfowl, 

 and I have shown in my book on Plant Dispersal (pp. 369, 513), not 

 only that the fruits of Potamogetons are to be found in the stomachs 

 of these birds, but that they germinate much more readily after 

 passing through a bird's digestive canal. This Potamogeton figures 

 on the island of Pico as an aggressive species that is gradually taking 

 possession of the mountain lakes and ponds and is ousting such 

 plants as Littorella lacustris and Isoetes lacustris (I. azorica, D.) 

 from the shallows. Doubtless it is a more recent arrival than the 

 two species just mentioned. As to the spores of Isoetes it may be 

 remarked that they were most probably brought in dried mud adhering 

 to the feet of birds of aquatic habits. The seed-like fruits of the 

 cyperaceous species that line the water's edge, Car ex flava, Scirpus 

 multicaulis, S. palustris, etc., were, it is likely, originally transported 

 in the stomachs of waterfowl. Wild ducks, as has been shown 

 in the work above quoted (p. 513), swallow the hard nutlets of 

 Cyperacece in quantities, and these fruits readily germinate after 

 being removed from the stomach and intestines. The fruits of 

 Scirpus palustris sink, but those of Carex flava buoyed up by the 

 utricle float for six months and more, and form a constituent of the 

 floating drift of ponds. 



4. The Modes of Dispersal of the Coast Plants. — The littoral flora 

 of the Azores is scanty owing to the coast being usually rock-bound. 

 We might have expected as in tropical regions that the currents 

 would have been important agents in stocking these shores with 

 their plants, but, unless we include the intermediate agency of the 

 drifting log, they have not taken a prominent part. In this respect 

 the littoral flora of the Azores behaves like the shore floras of temper- 

 ate latitudes (see Plant Dispersal, p. 33). The following are the 

 results of the writer's observations on the capacity of the seeds or 

 fruits for direct transport by currents. 



When the data are supplied by old experiments and observations 

 to be found recorded in the writer's previous book on Plant Dispersal 

 they are marked O. 



Beta maritima. — The nutlets sink in sea-water, but enclosed in 

 the perianth, whether fresh or dry, they may float for two or three 

 days (O). 



