It is different, however, with the flora which fringes beaches in the Tropics. Here many of the plants possess large fruits of great buoyancy, which are still afloat and alive after months of tossing on the waves, and if cast up germinate readily. These bold wanderers are a familiar feature of Tropic plant life, and their successful voyaging accounts for the uniformity of the beach flora on innumerable islands. Even our own inhospitable shores sometimes receive these waifs of warmer seas, brought from the West Indies by the Gulf Stream and the prevailing south-west winds. Of these the most frequent are the large bean-like seeds of _Entada scandens_, a Leguminous plant, which are originally enclosed in gigantic pods several feet in length, and the more globular seeds of the Bonduc (_Guilandina bonducella_), another species of the same order. But the most famous of all floating fruits is the Double Cocoanut, or Coco-de-mer, a huge nut weighing 40 or 50 lb. and containing several seeds a foot and a half long. It is the product of a Palm (_Lodoicea Sechellarum_); cast up on the shores of India, it was known centuries before its place of origin in the Seychelles was discovered, and fantastic legends grew up regarding it. 3. _Wind._--Everything that we know about the wind suggests that it is a potent agent of seed-dispersal, far excelling, for instance, that of flowing water. “All the rivers flow into the sea,” that cemetery of seeds, and their courses are at best mere spider-lines on a map. But the wind, blowing where it listeth, is everywhere, always ready to snatch up in its arms any seed of sufficient lightness, and to bear it away from the parent; in fancy we can see tiny seeds borne by gales across mountains and oceans. But we have to leave imagination out of account, and examine prosaically the mechanical laws according to which such transport is of necessity conducted. Any body liberated in still air will fall vertically with a velocity which increases according to well-known laws until the increasing resistance of the air to its passage equals the effect due to gravity; it thenceforward continues to fall at a uniform velocity, that velocity depending upon the nature of the falling body. In all seeds which are sufficiently light to be at all suitable for wind dispersal, the resistance of the air almost at once counteracts acceleration due to gravity, so that the rate of fall may be taken as uniform from the beginning. If the seed on liberation is carried along by the wind, it will acquire almost immediately the horizontal velocity of the air-current, but it will at the same time move downward through the air with the same velocity as if the air was still--just as a body dropped in a railway carriage will fall at the same rate whether the train is moving or standing still. If we measure the speed of fall of a seed in still air, then we can easily deduce the distance to which it will be carried by a horizontal air-current of