On Fig. 13 is delineated a very minute plant, called from its colour Chlorococcus. It may be found upon tree-trunks, walls, etc., in the form of green dust, and has recently been found to take part in forming the first stage of lichens. A large and interesting family of the “confervoid algæ,” as these low forms of vegetable life are termed, is the Desmidiaceæ, called in more common parlance desmids. A few examples of this family are given in Plate IV. They may be found in water, always preferring the cleanest and the brightest pools, mostly congregating in masses of green film at the bottom of the water, or investing the stems of plants. Their removal is not very easy, but is best accomplished by very carefully taking up this green slippery substance in a spoon, and straining the water away through fine muslin. They may also be separated by allowing a ring, covered with muslin, to float upon the surface of the water collected in a jar, for, being great lovers of light, they assemble where it is most abundant. An opaque jar should be used. For preservation, glycerine-gelatine seems to be the best fluid. A very full and accurate description of these plants may be found in Ralfs’ _British Desmidieæ_. Fig. 4 represents one of the species of Closterium, more than twenty of which are known. These beautiful objects can be obtained from the bottom of almost every clear pool, and are of some interest on account of the circulating currents that may be seen within the living plants. A high power is required to see this phenomenon clearly. The Closteria are reproduced in various ways. Mostly they divide across the centre, being joined for a while by two half-cells. Sometimes they reproduce by means of conjugation, the process being almost entirely conducted on the convex sides. Fig. 5 represents the end of a Closterium, much magnified in order to show the actively moving bodies contained within it. Fig. 16 is a supposed desmid, called Ankistrodesmus, and presumed to be an earlier stage of Closterium.