AMONG THE MANGROVES.

Auckland Star, Volume LXIV, Issue 283, 30 November 1933, Page 6

AMONG THE MANGROVES.

A BOTANIST IN FIJI. (By MARGUERITE W. CROOKES, M.A.) It was with very considerable eagerness that I awaited my first visit to a tropical mangrove swamp. I was also apprehensive, for our New Zealand mangrove swamps are apt to be somewhat noisome places which one contemplates with greater pleasure from afar. But the tropical mangrove swamp is very different. To begin with, some mangroves attain the height of forest trees, so that we have a forest rather than a swamp —a forest with all its implications of dignity and mystery. 1 used to love tile roadway through the swamp best when the tide was in—when all the silent winding channels brimmed with water so still that not a leaf was blurred. Along the bank multitudes of young mangroves grew in serried rank*, covering the swamp floor everywhere, and over all the fullgrown mangroves, gnarled and massive, spread their great green crowns in almost all parts, shutting out the sun. A quiet place, the mangrove swamp—very quiet and peaceful, its .silence broken mainly by the long-drawn haunting call of the honey-eaters, the soft rustling of' brightly-coloured soldier crabs scuttling to their holes, or the sudden soft "plop" as a long, green mangrove fruit detached itself and dropped 011 to the quiet tide. And strange indeed those fruits are, like many other things about the mangroves. It is a good old Anglo-Saxon proverb that says you cannot have your cake and eat it. Well, if you' happen to be a tree you cannot expect to live a pleasant, amphibious life in situations where few others will venture to compete with you, and at the same time enjoy all the ease and security of orthodox life 011 land. There are all sorts of difficulties about the amphibious environment, and the mangroves have their own way of meeting them. More Air!

There are in Fiji two main kinds of mangrove, those belonging to the family Rlvizopliora, and those belonging to the family liruguiera. Rhizophora means "literally "rootbearing," and you do not need to look closely at the plant to understand the name. The Rhizophora flings down quantities of aerial roots from its branches, even from its highest ones. Now this mass of roots gives the mangrove a most bizarre appearance; in some cases they give them the aspect of having spindly legs, not unlike gigantic stick insects. These roots not only give the mangrove secure foothold among the moving water, but they also serve the very useful purpose of enabling it to augment its supply of oxygen. Salt mud may be very cool and damp, but it is not the l>cst aerated thing in the world. Our own New Zealand mangroves deal with the oxygen shortage in quite a different way. Instead of sending roots down from above they send roots up from below, lience the slimy little "pegs" that are so annoying if one is trying to cross the swamp barefoot.

But having safeguarded, its own foothold in the mud or coral sand, the mangrove lias a still graver difficulty to deal with. ITow can it safeguard the interests of' its children? The situation is a complicated one. In the first place, tho fruits are likely to fall 011 to the moving tide; in the second, how ean they root 011 ground that is being constantly covered by moving water? On the one hand, they must be prevented from drowning, on the other hand, they must be given some means of gaining a foothold in their slippery home. Trials of Infancy. Not content with tho formation of a fruit in tile ordinary way, the tree actually produces a young plant. The. seed germinates whilo still attached to the tree, and grows steadily till it is several incites long. At this stage it is a sturdy cylinder, shaped somewhat like a big, green cigar. It is now finally cast forth from the parent, and left to fend for itself. Various interesting provisions have, however, been made for its future. In the first place, mangrove seedlings arc able to float. Not only that, but they float in a vertical position. Thus on calm, hot days they are to a very considerable extent protected from the sun's rays. Their weight, however, is so nicely balanced that while they float upright in salt water they become horizontal in fresh. Cast forth upon the water, the seedlings of Rhizopliora can float unharmed for three or four months, those of <Brnguiera for even longer. Once established in a suitable position, they strike very quickly and soon become flourish - ing young plants.

Final Explanations. Even from this brief and of necessity superficial sketch my reader will gather by what delicately adjusted means the mangrove fits itself to its chosen surroundings. How, then, shall we regard the mangrove? As one of the most specialised "up-to-date" plants, that has by slow degrees fitted itself for the exigencies of amphibious life? Mr. Guppy, however, that fascinating authority on the Western Pacific, has other views. The mangroves, lie thinks, arc essentially survivals. They come down to us a remnant from a far-distant past, a past when the earth was clothed in dank and clinging mist that stifled out the sun, a past when no human voice had yet troubled tho immemorial solitudes. At that time, thinks Guppy, tho germination of seedlings while still attached to the plant was not the exception but tho rule. Then with the slow r passing of tho ages 'the climate ofi the earth gradually changed, and it is only in such situations as those represented by the chosen habitation of tho mangrove swamp, that something resembling tho old conditions still remains.