suppose that the almost infinitely numerous icebergs, charged with great masses of rocks, soil and _brushwood_{368} and often driven high up on distant beaches, might have been the means of widely distributing the seeds of the same species? {366} In the margin the author has written "(Forbes)." This may have been inserted at a date later than 1844, or it may refer to a work by Forbes earlier than his Alpine paper. {367} See _Origin_, Ed. i. p. 367, vi. p. 517. {368} <Note in original.> Perhaps vitality checked by cold and so prevented germinating. <On the carriage of seeds by icebergs, see _Origin_, Ed. i. p. 363, vi. p. 513.> I will only hazard one other observation, namely that during the change from an extremely cold climate to a more temperate one the conditions, both on lowland and mountain, would be singularly favourable for the diffusion of any existing plants, which could live on land, just freed from the rigour of eternal winter; for it would possess no inhabitants; and we cannot doubt that _preoccupation_{369} is the chief bar to the diffusion of plants. For amongst many other facts, how otherwise can we explain the circumstance that the plants on the opposite, though similarly constituted sides of a wide river in Eastern Europe (as I was informed by Humboldt) should be widely different; across which river birds, swimming quadrupeds and the wind must often transport seeds; we can only suppose that plants already occupying the soil and freely seeding check the germination of occasionally transported seeds. {369} A note by the author gives "many authors" apparently as authority for this statement.