Clare Island Survey — Phanerogamia. 1 79 



It will be seen that as a whole the plume seeds experimented with are 

 better adapted for wind-dispersal than either the wing seeds or powder seeds. 

 Of the plume seeds, the place of honour belongs, not to the group with 

 elaborate parachutes, but to Typha latifolia, which is followed — at some 

 distance — by the Epilobiums and Willows ; these in buoyancy slightly 

 exceed the best of the Compositae, which form a long series extending down 

 to species quite devoid of parachute apparatus. Eriophorum angustifolium 

 is nearly equal in efficiency to the most buoyant of the Compositae, and in 

 relation to the same group, such seeds as Clematis Vitalba, Dryas octopetala, 

 and Trifolium arvense occupy a low place, and are possibly chiefly useful in 

 promoting dispersal by animals. 



As regards wing seeds, the best of them, such as Ulmns montana and 

 Pirms sylvestris, cannot compare with even the second or third grade of 

 the plume seeds. Ash and Sycamore are again far behind Elm and Pine ; 

 while, in the case of wing seeds such as the Docks, the appendages must 

 be much more useful in promoting dispersal by animals than in aiding wind- 

 dispersal by checking the velocity of fall. 



Coming to the powder seeds, we find that mere reduction in size is not 

 carried far enough in the Flowering Plants to produce an efficient dispersal 

 device. The small hard roundish seeds that occur in so many species fall 

 with a high velocity. They have a high specific gravity — all which were 

 tested sinking at once in water — and they possess no device for restraining 

 their rate of fall. Elongated seeds, such as those of Hypericum and J uncus, 

 have a rather lower rate of fall (occasioned in part by a less specific gravity). 

 The great elongation in the case of Narthecium has a marked effect in this 

 direction. It is only in Orchidaceae, where minuteness is combined with 

 looseness of tissue, that (among Phanerogam powder seeds) a really low rate 

 of fall is found ; but even these seeds cannot compete as regards buoyancy 

 with the more efficient of the plume seeds. A few of the larger roundish 

 seeds, such as those of Brassica Bapa, Lathyrus pratensis, and Scilla verna, 

 tested for comparison, have a very high velocity, falling 40 feet in between 

 1 and 3 seconds. 



To get an idea of what are the possibilities of seeds reaching Clare Island 

 by the agency of wind, let us take a very favourable case. A seed with a high 

 index of efficiency — say, Epilolium montanum, which takes 20 seconds to 

 fall 12 feet (an efficiency even higher than that of any Composite parachute 

 seed) — is liberated at a spot within 5 miles of the island, with a favourable 

 gale blowing at 50 miles per hour. The seed would take only 6 minutes to 

 traverse the horizontal distance ; but during that time its fall would amount 

 to 216 feet. This represents the height to which the seed must be raised by 



