PLUME SEEDS 69 
those of almost any Composite, while by far the most 
buoyant seed in the British flora is that of the Reed- 
mace (Typha). In this case the seed itself is minute, 
and is situated on a very slender stalk, from near the 
base of which springs a tuft of delicate hairs. This 
seed takes thirty-four seconds to fall twelve feet. 
Using once more the Azorean example, it could cross 
the 800 miles of sea if it had an initial elevation of 
34 miles, or was raised to that amount during the 
sixteen hours occupied by its passage. 
Summing up, then, we find that the plume seeds are 
the most efficient of all seeds for extended flights by 
the agency of the wind. If the efficiency of the seeds 
of the Reed-mace, the most buoyant among British 
plants, be taken as 100, the efficiency of the Willow- 
herbs is between 60 and 70, of Willows 45 to 70, the 
best of the Thistles 35 to 40, Dandelion 25. Even the 
best of the winged seeds are much less efficient, Elm 
and Scotch Fir being about 20, Sycamore and Ash 
9 or 10. Of powder seeds, the efficiency of several 
Orchids tested ranges from 35 to 65, and Broomrapes 
(Orobanche) from 20 to 25. Most of the powder seeds 
are far below these, the efficiency of seeds of Papaver 
dubium, for example, being only 4°5 on the same scale. 
This last figure is representative of the many small- 
seeded plants in the British flora such as are found 
among the Crucifere, Caryophyllacee, Scrophu- 
lariacee, etc. The relative efficiency of such compara- 
tively large seeds as those of many of our Legumin- 
ous plants would be about 1 on the same scale. 
4. Dispersal by Animals—The coverings of many 
seeds are provided with hooks or barbs, and others 
with stiff hairs, which render them liable to become 
