24 
POPULAR SCIENCE REVIEW. 
nature of surrounding circumstances, easily supply us with an 
intelligible reason for the act. But it is more difficult to 
account for the migration of plants, intimately connected as 
they are with the soil; and if, nevertheless, we find these 
effecting a migration from one continent to the other, it can only 
be the result of a tendency belonging less to the individual 
than to the whole species struggling for existence. If it be 
interesting to trace the migrations of different races of men 
and animals, it is not the less so to watch the distribution of 
plants. At present a considerable number of European plants 
grow in New Holland, and many of them existed there even 
before that continent was discovered by us. If these could 
find their way thither across the equator, New Holland plants 
could pass to us before vessels began to navigate between the 
two continents. What currents, winds, and migratory animals, 
can effect in this respect has been substantiated by super- 
abundant evidence. Long ago. Nature established a telegraphic 
intercourse over the globe, by means of which she not only 
makes known her decrees, but effects her necessary postal 
communications ; and if amongst the cosmopolitan plants there 
are so many lower Cryptogams propagated by minute light 
spores, we cannot long remain in doubt about the agents 
that lent a helping hand to these colonists. But even this, 
as everything else in this world, has its limit ; and it would be 
unphilosophical to think that by these means alone we could 
explain the whole distribution of plants. Oceans and large basins 
of water offer, indeed, great obstacles to the spreading of terres- 
trial plants, though they may be instrumental in carrying 
fruits and seeds. But experience has taught that the trans- 
portation effected by waves and currents is, afc best, confined 
to only a limited number of plants which can bear the ill 
effects of water without losing their vitality, and which, on 
their arrival on foreign shores, meet with such conditions as 
are essential to their existence. It is evident that amongst 
the numerous species composing the flora of a country there 
can only be very few which are able to overleap the boundaries 
of their natural range. 
But all this does not explain how the peculiarities of a whole 
flora can reappear in far distant countries. If, therefore, we 
find in the Eocene flora of Europe principally plants bearing* 
the characters of those of Australia and Polynesia, we can 
hardly believe that the whole of them could have passed un- 
injured across Torres Strait to New Guinea, the Moluccas, 
&c., to Asia, and thence to Europe. On the contrary, to 
render this singular fact somewhat intelligible we shall be 
compelled not only to assume a closer connection of the 
different Polynesian islands with Australia, but also a conti- 
