By far the most extraordinary of all these plants which form new land are the Mangroves.
They are only found in the tropics or sub-tropical regions, and are always along the sea-coast. It is where a river ends in a delta, dividing into intricate and confused irregularly winding creeks, that the mangroves are especially luxuriant.
Such a river will have probably flowed through hundreds of miles of the most exuberant tropical forest, where growth is never checked by the cold grasp of winter.
Its waters are yellowish brown or café au lait coloured, because they are full of mud and of decaying vegetation, with dead leaves and decaying branches floating on the surface. So full are such rivers of decaying material that they have a distinct and unmistakable smell, which has been compared to "crushed marigolds."
So soon as the muddy water reaches the sea, most of its mud is deposited and forms great banks and shoals of shifting odoriferous slime, which confuses and interferes with the discharging mouths of the river.
It is upon these changing, horrible-smelling banks of bottomless slime that the Mangrove is especially intended to develop.
If one takes a canoe in such a delta and paddles inwards on the incoming tide, a dense forest of glossy-green mangroves will be found to cover the whole coast-line, and also to extend far inland by the winding creeks, lagoons, and river channels.
The whole theory of the mangroves becomes clearly revealed as soon as the water begins to sink at low tide. First one notices that the stem of every mangrove ends below, not in a single trunk, but in an enormous number of arched, stilt-like supporting roots. Not only the stem but the branches also give off descending roots, which branch into four or five grasping arched fingers as soon as they get near the water. When they reach the mud, these fingers grow down into it and form a new supporting root to the tree. It is very difficult to give any idea of the extraordinary appearance of these mangrove roots.
Imagine an orchard of very old apple trees in winter, and suppose that one were to cut off every tree and plant it upside down in black mud, and also to crowd them so closely together that the branches were all mixed and confused. This may give an idea of the odd and strange appearance of the root-system in a mangrove forest. Upon these arching roots, even on those which are not yet attached, multitudes of oysters may be seen. There is also a little fish (a sort of perch) which climbs up on to the roots or out of the mud below, and gasps or squatters about in it.
As to the mud itself, it is a horrible, greasy, oozy, black or blue-black slime of bottomless depth. "It is full of organic, putrefying, strongly-smelling material, clearly full of bacteria. The water itself is sometimes covered by a dirty, oily scum, and air-bubbles rising from the bottom, spread out on the surface and let loose their microbes in the atmosphere."[74] There are many crocodiles, which may be seen reposing on the mud above high tide. It is difficult to distinguish them from a rough log of wood, but it is still more difficult to kill them, for their scales turn any ordinary bullet. There is scarcely any experience more exasperating than when, after one has taken a long, careful, and accurate aim, one observes the sleeping brute suddenly wake and scurry down into the water with a hideous leer on its face. Sea-cows or manatees are said to live in these creeks. Little ducks of many kinds rise in hundreds and thousands, but the commonest bird is the "curlew" (either a whimbrel or closely allied to it). During the day they sift the mud with their long curved beaks for insects, and at sunset fly down in vast numbers to the mudbanks near the sea. A miserable little white crane called "Poor Joe" is common, and has the same habit. It is not worth shooting, and it is quite aware of the fact. Herons, cormorants, and other birds are often to be seen. Monkeys sometimes visit the mangroves, probably to eat oysters or crabs. There are several kinds of crablike creatures which climb up the roots and may be seen running about all over them. But during the three weeks spent by the writer in the Mahéla creeks of Sierra Leone, it was the insects that made the deepest impression upon him; as soon as the evening falls the mosquitoes appear in myriads and in millions. Such creeks and mangrove swamps are always feverstricken and dangerous, and probably enjoy the very worst climate in the whole world. Of course nowadays, when Sir Patrick Manson and Dr. Ross have discovered that the mosquito carries the malaria germ, it is possible with great care to guard against malaria. One has also the satisfaction of knowing that the mosquito itself cannot be perfectly at ease with all these tiny parasites attacking its digestive organs.