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Résumé :
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The sequence of topics is deliberately chosen to deal first with a brief survey of the physico-chemical backgroung (chapter 1), followed by a general discussion of the habitats and communities (chapter 2). then habitats exposed first to rainwater as it falls, through increasing salinity and complexity due to percolation, flow and interaction of the water with sediments, etc. are discussed in more details. thus, chapter 3, deals with the flora of bare rock surfaces on mountains subjected almost entirely to rainwater, then with that of the rock surfaces of streams, rivers and lakes and finally with the flora of the rocky sea shore. a similar but geographically restricted habitat involves the free-living species of the algal community of coral reefs and this is dealt in chapter 4. the breakdown of the rock ands its intermixture with organic matter to give soil, and underwater sediments provides the next habitat group on the land surface, in rivers, lakes and shallow seas, all richly colonised by algae (chapter 5). the water which has percolated, seeped and drifted past all these communities then collects in rivers, lakes and the open ocean and there surface layers are colonised by the phytoplankton (chapter7). the remaining chapters deal with certain general and inter-linked aspects - dispersal and phytogeography (chapter 8), symbiosis-parasitism-grazing (chapter 9), seasonal succession (chapter 10), energy flow and cycling of nutrients (chapter 11), sedimentation of algal remains (chapter 12), palaeoecology (chapter 13), and finally eutrophication and pollution (chapter 14).
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