A very common plant is to be found, either growing in little tufts on the rocks at low-tide mark, or as a waif cast up by the waves, in bunches, near where the coast contains rocks or earths which have carbonate of lime in them. It is also a dweller in deeper water on the floor of the sea, and oftentimes it may be seen waving lightly in a rock-pool; but it does not look like a plant. There are no leafy fronds, and it does not resemble any other common sea-weed in outside appearance. It has a stony look, and is hard to the touch; it will stand a pinch, and although it may break into separate pieces it can hardly be crushed by the finger and thumb. Usually, as seen by most people, it is of a glistening white color, with some purple about it, and is made up of a number of joints. The coralline, for so it is called, has a sort of broad crust where it adheres to the rock, which gives out a stem. This stem is slender, and is made up of many pieces, placed one before the other, narrow where they join, and rather swollen in the middle or at the end. Other pieces, usually two, come off from the piece at the joint, and there may be hundreds of them or only a few. The end of the plant is made up of tufts of pieces, some of which have a little hole in the end, as if there were a hollow place. Now, if the spots where the pieces join be looked at carefully, there appears to be something like very thin threads uniting one piece to another, and they are not covered, as all the rest is, with the glistening white stuff, which feels gritty between the teeth. These corallines, if placed in vinegar, begin to bubble as if they were made up of chalk, and their outsides are composed of a mineral called carbonate of lime. After a while the vinegar dissolves all the hard white part, and leaves the threads, which are now seen to run the whole length of the coralline. These threads are portions of vegetable fibre, and constitute the inside stem as it were, which is surrounded by a sort of bark of carbonate of lime. [Illustration: Lichens and Small Fungi 1, Lecanora; 2, Opeographa; 3, Parmelia; 4, Cetraria Islandica; 5, 11, Cladonia; 6, Usnea Barbata; 7, Red Wart Fungus; 8, Pertusaria; 9 Bæomyses; 10, Erysiphe; 12, Cyanthus]