. Plants of New Zealand. the breakwaters formed ofsingle posts, which may be seen in many English run sometimes in straight lines, sometimes in curves,and sometimes in Vandykes. Usually, they are from two tofour inches apart, but in some places the mud is so thicklystudded with them, that it would be scarcely possible to slip apencil between. When the tide is coming in, or when a floodcomes down the creek, these vertical pegs greatly break theforce of the water. They are exceedingly elastic, and springback at once into an upright position if a heavy weight isplaced upon them and
. Plants of New Zealand. the breakwaters formed ofsingle posts, which may be seen in many English run sometimes in straight lines, sometimes in curves,and sometimes in Vandykes. Usually, they are from two tofour inches apart, but in some places the mud is so thicklystudded with them, that it would be scarcely possible to slip apencil between. When the tide is coming in, or when a floodcomes down the creek, these vertical pegs greatly break theforce of the water. They are exceedingly elastic, and springback at once into an upright position if a heavy weight isplaced upon them and then removed. Not content withkeeping back the flood, they gather in their myriad rootlets, asin a sponge, all the silt and sediment that is brought down bythe rivers. The thick mud settles and cakes among the rootfibres, while the pegs hold back any sticks, straws, or rubbishafloat in the water. The fibrous matting between the pegs israrely laid bare, save after a heavy flood, and spreads widely, THE VEEBENA FAMILY 359. Fig. 118. Seeds of Avicenuia officinalis. 360 PLANTS OP NEW ZEALAND forming a huge disk that prevents the mangrove from beingupset. The tree is further propped up by a number of stiltroots. These, however, are not so large or so long as in thetypical mangrove {Uhizopliora mangle) of the tropics. The trees, thus buttressed, stayed, and fixed by their variedroots, stand firm in the highest tide and the strongest flood,and gather about them material for a rich soil, whichgradually becomes suitable for cultivation. Then they stepfarther out into the water and begin their work again. So faras can be roughly estimated, the mud-flats are thus raised bythe action of the mangroves, on an average, a little over aninch each year. This rate of speed is probably only that of thepresent time, as it must have been much slower in past years,before the bush was so extensively cut. Since the clearing ofthe land, slips have become much more frequent, and hencethe rate of depositi
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplants, bookyear1906
