78 
ISLAND LIFE. 
[part I. 
for migration have been pointed out by eminent botanists, and 
a considerable space might be occupied in giving a summary of 
what has been written on the subject. In the present w r ork, 
however, it is only in two or three chapters that I discuss the 
origin of insular floras in any detail ; and it will therefore be 
advisable to adduce any special facts when they are required to 
support the argument in particular cases. A few general 
remarks only will therefore be made here. 
Special adaptability of Seeds for dispersal . — Plants possess 
many great advantages over animals as regards the power of 
dispersal, since they are all propagated by seeds or spores, which 
are hardier than the eggs of even insects, and retain their 
vitality for a much longer time. Seeds may lie dormant for 
many years and then vegetate, while they endure extremes of 
heat, of cold, of drought, or of moisture which would almost 
always be fatal to animal germs. Among the causes of the 
dispersal of seeds De Candolle enumerates the wind, rivers, 
ocean currents, icebergs, birds and other animals, and human 
agency. Great numbers of seeds are specially adapted for 
transport by one or other of these agencies. Many are very 
light, and have winged appendages, pappus, or down, which 
enable them to be carried enormous distances. It is true, as 
De Candolle remarks, that we have no actual proofs of their 
being so carried ; but this is not surprising when we consider 
how small and inconspicuous most seeds are. Supposing every 
year a million seeds were brought by the wind to the British 
Isles from the Continent, this would be only ten to a square 
mile, and the observation of a life-time might never detect 
one ; yet a hundredth part of this number would serve in a few 
centuries to stock an island like Britain with a great variety of 
continental plants. 
When, however, we consider the enormous quantity of seeds 
produced by plants, — that great numbers of these are more or 
less adapted to be carried by the wind, — and that winds of great 
violence and long duration occur in most parts of the world, w T e 
are as sure that seeds must be carried to great distances as if 
we had seen them so carried. Such storms carry leaves, hay, 
dust, and many small objects to a great height in the air, while 
