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Show 358 GEOGRAPHICAL DISTRIBUTION. CHAP. XI. with each other, and with the many existing oceanic islands. Several facts in distribution, -such as the great difference in the marine faunas on the opposite sides of almost every continent,-the close Telation of the tertiary inhabitants of several lands and even seas to theiT pTesent inhabitants,-a ceTtain degree of Telation (as we shall heTeafteT see) between the distTibution of mammals and the depth of the sea,-these and other such facts seem to me opposed to the admission of such prodigious geographical Tevolutions within the recent period, as are necessitated on the view advanced by Forbes and admitted by his many followers. The nature and Telative proportions of the inhabitants of oceanic islands likewise seem to me opposed to the belief of their foTmer continuity with continents. Nor does their almost universally volcanic composition favour the admission that they are the wrecks of sunken continents ;-if they had originally existed as mountain- ranges on the land, some at least of the islands would have been formed, like other mountain-summits, of granite, metamorphic schists, old fossiliferous or otheT such rocks, instead of consisting of mere piles of volcanic matteT. I must now say a few words on what are called acci-dental means, but which more properly might be called occasional means of distribution. I shall here confine myself to plants. In botanical works, this or that plant is stated to be ill adapted for wide dissemination; but for transport across the sea, the greater or less facilities may be said to be almost wholly unknown. Until I tried, with Mr. BeTkeley's aid, a few expeTiments, it was not even known how far seeds could resist the injurious action of sea-water. To my surprise I found that out of 87 kinds, 64 germinated afteT an immeTsion of 28 days, and a few survived an immersion of 137 days. CuAP. xr. lliEANS OF DISPERSAL. 359 For convenience sake I chiefly tTied small seeds without the capsule or fruit; and as all of these sank in a few days, they could not be floated acToss wide spaces of the sea, whether or not they were injured by the salt-water. Afterwards I tried some larger fruits, capsules, &c., and some of these floated for a long time. It is well known what a difference there is in the buoyancy of green and seasoned timber; and it occurred to me that floods might wash down plants or branches, and that these might be dried on the banks, and then by a fresh rise in the stream be washed in to the sea. Hence I was led to dry stems and branches of 94 plants with ripe fruit, and to place them on sea water. The majority sank quickly, but some which whilst green floated for a very short time, when dried floated much longer; for instance, ripe hazel-nuts sank immediately, but when dried, they floated for 90 days and afterwards when planted they germinated; an asparagus plant with ripe berries floated for 23 days, when dried it floated for 85 days, and the seeds afterwards germinated: the ripe seeds of Helosciadium sank in two days, when dried they floated for above 90 days, and afterwards germinated. Altogether out of the 94 dried plants, 18 floated for above 28 days, and some of the 18 floated for a very much longer period. So that as fr seeds germinated after an immersion of 28 days; and as y! plants with ripe fruit (but not all the same species as In the foregoing experiment) floated, after being dried, for above 28 days, as far as we may infer anything from these scanty facts, we may conclude that the seeds of nfo plants of any country might be floated by sea-currents during 28 days, and would retain their power of germination. In Johnston's Physical Atlas, the average r~te of the several Atlantic currents is 33 miles per diem (some currents running at the rate of 60 miles |