"The most significant thing about all lichens is that they are two plants, not one. Each lichen plant body or 'thallus' is a biological twosome composed of a fungus living in intimate contact with an alga. The relationship involves much more than the mere contact or even relative position of the constituents; it results in the formation of the entirely new, self-sufficient, functioning unit which gathers raw materials, manufactures food, conducts an exchange of of vitamins and growth substance

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