(c) : Some algae withstand or tolerate a very high temperature and these are often called thermal algae. Such forms are known to grow upto 85°C, nearly boiling water. Their cell wall is hard and protective. A typical cell wall of algae consists of two nonliving layers. The inner layer is firm consisting of microfibrils and outer layer is gelatinous and amorphous. Various polysaccharides such as cellulose, pectin, mucilage constitute the typical cell wall. The mucilage covering of the cell is thick and dense and is called the sheath. This sheath holds the cells in colonies together, is having water absorbing and water retaining capacity. It thus protects them under dessicating conditions. Thus they are able to survive under high temperature.