Typical plants are holophytic, that is, they obtain their food substances from purely mineral sources.
Therefore all life in the sea (as on land) depends on the power which the holophytic organisms possess of synthesizing mineral substances into organized tissues.
Nutrition is of course holozoic or saprophytic in the colourless forms, holophytic in the coloured; but these divergent methods are exhibited by different species of the same genus, or even by individuals of one and the same species under different conditions.
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