Gelidium, Gracilaria, Pterocladia are red algae having industrial importance. They produce a jelly like substance agar-agar, used as culture medium with a number of different uses. Chlorella, a green alga contains 50% protein, vitamins. Antibiotic chlorellin has been extracted from Chlorella, found to be more effective against bacteria. Spirogyra, a green alga is also known as water-silk.