CORAL REEFS
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-—'probably the most widespread ofŒeef-building corals—
appears, for example, as a much branched, arborescent '
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coral in smooth waters (Plate 65), as a single cylinder often
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of great length in deeper- water, and as a solid, irregular
mass in the rough water on the outer edge of the reef within
the action of the perpetually pounding surf.
The reaSon
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for these varied forms is to be found in the inuence of these
different conditions on the growth processes of the coral;
in deep water which is always calm,athere is nothing to
prevent the original coral from developing on the “ ideal ’.’
plan and growing straight upwards with a single apical
point of growth from which polyps are budded 0' on all
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Sides, but inthe rather rougher conditions nearer the surface
even in the most sheltered conditions,-injury of the apical
polyp leads to the establishment of’nèw points of growth,
each of which forms a new branch,whe in the‘most exposed
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conditions perpetualinjury of all projectinggrowths leads
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to the formation of a solid, irregu‘lar maSs.
At one time
it was thought that these different types were all different
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kinds of corals, but now we know that many so—‘called
species ”are only varieties. due to the environment. The
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most strikingexample is that of the hydroid coral, Millepora,‘ ._
of which there are all manner of different—forms but ap,
parent-ly only the one species in the world.
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The effect of sediment is of the greatest importance.
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The coral polyps aieable to expand and contract, and their
exposed surfaces are usually covered with ne, rapidly
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moving hairs, the action of which helps to cleanse the
surface, but these are their only means of protecting them—
sediment and, like all attached 'animals, they
at the mercy of material which drops on «them
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above or -collects around them. A branching coral
growth has less
from falling sediment than a massive
growth:wbichoem a”wide surface on which :it can collect.
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