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tlie botauy of the second German Polar Expedition (GefässpH , p. 26) tliink this to 
be too hold an hypothesis, but still are inclined to accept it for the species pecu- 
liar to the northeastern eoast of Greenland. The hypothesis of transport by cur- 
rents, indeed, affords an easy explanation of facts of distribution, otherwise very 
difficult to account for, but it lias one very weak point — it has never been shown, 
not even in a single case, that a species has been introduced by this means. When 
Gkiskbach formed ins opinion about the question, very Httle was known even about 
the possihihty of seeds retaining their vitahty during a longer immersion in salt 
water, only a few experiments being made by Beukelef, Darwin, and Martins, 
but in låter ^times more comprehensive investigations are tnade, for instance by 
Birger and Åkerman. 
The result of these experiments may be summed up as showing the fact, that 
a considerable number of species of different famihes are able to stånd soaking in 
seawater for a month or more without losing their power of germination, and that 
a smaller proportion of them float on the water for a more or less considerable 
time. The difficulty of so many seeds siuking after a short immersion may, how- 
ever. be overcome, as they may be floated in the capsules, on driftwood, and 
what is most important in the Polar Sea, on ice. But there is still one important 
difliculty left, viz., the transport of a seed, cast up on the beach, to a convenient 
place of growing. This makes the question of migration different from that of 
transport, for as in many instances the seed of a plant can Ii ve in seawater, but 
the plant canuot stånd salt water in the soil, the seed has to be transferred from 
•the beach inland before it germinates, if it shall thrive and actually become a new 
citizen of the land where it has arrived in the drift. In the case of ice acting as 
a raft for the transport of seeds there is still another point that seems overlooked 
by Grisebach and other advocates of the migration by means of drift. Seeds, as 
well as other matter lying on the ice will absorb the heat of the suiJight and thus 
come to sink rather deep down in a hole melted below the surface. Here they 
will lie innnersed in fresh water and get swelled, perhaps also they may grow, and 
if the ice is not dissolved and the seed cast up on a beach in the same summer, 
they will freeze in, perhaps to get melted out again in the next summer. In the 
case of a long transport, such as across the Polar Sea from Siberia to Greenland, 
this may be repeated perhaps five or more times, and for my part I do not believe 
any seed to be able to survive such a voyage. 
Even if the importance of the ice as a means of transport over wide ex- 
panses of sea is declined, it does not follow, however, that it may not occasionally 
help plants to cross narrow channels or fjords. I have seen, more than once, 
vegetable matter heaped on seaice in such quantities, as to protect the ice from 
meltmg, and once at least I found accumulations of leaves, stems of different plants, 
tufts of moss, fragments of lichens, etc, lying several inches thick and quite dry 
on tiie surface. I iiad no opportunity of examining it closer, but I saw fruits of 
Dryui^ among the other matter, and there may have been seeds of different plants 
