MEETING OF THE BRITISH ASSOCIATION. 27 
ditions, though they agreed on two most important points. These 
were — 1. That the continental plants were not separately created on 
the continent and islets, but passed from one to the other. 2. That 
insular floras were more ancient than those of continents. This last 
proposition was proved by the Atlantic plants of Madeira, the Cana- 
ries, and Azores, belonging to genera, and perhaps species, that existed 
in Europe during the Tertiary period, but which have since then be- 
come extinct on that continent. 
The first hypothesis is that of the late Professor Edward Forbes, 
who supposed that the continents once stretched across the ocean, so 
as to include the islands, which were thus peopled with plants by in- 
termediate land which has since disappeared. This hypothesis was 
propounded at the Cambridge meeting of the British Association in 
1845, and, having been amply discussed there and elsewhere, the 
lecturer did not deem it necessary to recapitulate the arguments in 
favour of it. 
The other hypothesis, that the plants had been carried by birds or 
the elements from the continents to the islands, had long been held as 
a supposition, but never developed scientifically till Mr. Darwin did so 
in his 'Origin of Species.' Mr. Darwin's principal arguments are: 
That all naturalists admit such transport to exist, however limited in 
degree; that birds do carry seed, etc., and that Madeira and the 
Azores are stocked with European birds; that birds annually pass 
from America to Europe, and from Europe to Greenland ; that as 
fish devour seeds, and birds fish, the birds may thus carry the seeds to 
distant islands ; that dust is blown across the Atlantic, and that many 
seeds are no larger than particles of dust; that many seeds will bear 
long immersion in salt water without losing their vitality, and are 
often transported by marine currents; and that coral islets are con- 
fessedly thus peopled with plants, however far from land. Of negative 
evidence, Mr. Darwin adduces— That oceanic islands are poor in 
species; that whole Orders of plants are absent from them ; that land 
mammals and batrachians are not to be found in oceanic islets, but 
that winged mammals, birds, and insects are found in all; and that if 
continental extension is granted to one island, it must be to all, which 
is inconsistent with probability, and with the fact that so many are vol- 
canic. Lastly, Mr. Darwin shows how many facts and phenomena of 
insular floras may be explained by assuming the hypothecs of trans- 
