However, suppose yourself seated on a grassy cliff near Eastbourne or Brighton.
Looking lazily out over the blue waters, you see Norwegian timber ships and steamers of all kinds, from the little coasting "Puffing Billy" to the huge liner departing for Australia or South Africa.
Plants are probably using every steamer; in the straw of the packing cases, in the cargoes of corn or grain, in the ore, and in the ballast, there are sure to be seeds. Such stowaways are mostly weeds, but of course many valuable garden, farm, orchard, and forest seeds are being intentionally exported.
Looking down on the seashore, you will notice the high-water mark, a yellowish brown line of floated rubbish which is quite distinct even at a distance. If you now go down and examine it closely (not a particularly pleasant operation, seeing that so much is in a decomposing condition) you will find many seeds amongst the corks and bits of straw, seaweed, and objectionable, if lively, animalcula, and very likely also pieces of plants, such as willow branches, which might quite easily take root.
On the coast of Norway, and on our own western seaboard, the fruits of a West Indian bean (Entada scandens) are occasionally to be found, and its seeds are probably able to germinate. We know that in long-past geological ages they were floating round the estuary of the Thames, where they occur as fossils. It has been found by experiment that fruits and seeds are not killed although they have floated for a year or more in salt water. Thus ocean currents are utilized to carry fruits and seeds.
But from our comfortable seat on the South Downs, still more can be learnt of wandering seeds. The wind which blows across the downs carries with it hundreds of winged or hairy fruits, all of them exquisitely fashioned as miniature airships, aeroplanes, or other winged contrivances. The wind is an important distributer of seeds.
One of the South Down sheep is trailing behind it a piece of bramble which has caught in its wool; others, which have been grazing on the broken cliff-edge where Agrimony, Forget-me-not, and Burdock are flourishing, are certain to have spiny or sticky fruits entangled in their wool. Animals therefore carry seeds in their wool or fur. If it should happen to be a fine, sunny afternoon, and if there are any plants of Broom near by, it is quite likely that you may, every now and then, hear a faint, sudden crack. This will be the Broom at work scattering its seeds by itself. The little pod, when it dries, contracts in such a way that it splits with a sudden explosive pop, and the seeds are sent flying to a distance of three or four feet. This curious fact was observed in 1546 by the naturalist Boek. The Whin and many other plants act in the same way, for the dry fruit becomes elastic and coils up spirally, flinging away the seed.
But here also, on the southern shore of England, we are at a main station of arrival and departure for migrating birds. A Landrail or other marsh bird might be flushed in France, and might quite easily cross the Channel with French mud sticking to its plumage. In this mud, or in its crop, there may be seeds or fruits which will be left in an English pond. This method is probably a very important one, for these plants growing in duck-haunted places are amongst the most widely distributed of all.
Mr. Reid has a very interesting discussion on this point. The crow or rook could quite well cross the British Channel now. In the days when Britain was covered with ice and snow, the gap between the French and the English shore was only half the present width. There was at that time much flat land with oak forest bordering the French coast.
Mr. Reid shows that it is probable that rooks regularly carry about acorns in the cup, for he found seedling oaks associated with empty acorn husks, stabbed and torn in a peculiar way. "On October 29th of 1895, in the middle of an extensive field, bordered by an oak copse and scattered trees, I saw a flock of rooks feeding and passing singly backwards and forwards to the oaks. On driving the birds away, and walking to the middle of the field I found hundreds of empty acorn husks and a number of half-eaten, pecked acorns."[114] So that crows may have brought the acorns that colonized Britain with oak forest in the earliest historical period.