Pond life is rich in subjects for the microscopist. Any stagnant pool may contain organisms which will delight the naturalist who has always depended upon his unaided vision. Curiously enough, amongst the most wonderful of all these pond-dwelling plants are the Diatoms, which consist of but a single cell. They are so numerous, they exist in so many different forms and in so many different situations that were we able to describe them all, we should require the whole of a large volume, much larger than this. In colour, Diatoms are usually brown or brownish, although they contain chlorophyll, the green colouring matter of higher plants. In shape they may be rod-shaped, crescent-shaped, circular, wedge-shaped, oblong or oval. Some float about freely in the water, some are attached to supports by means of stalks. Some lead a solitary life and others dwell together in colonies. One feature they have in common, a curious flinty cell wall, and this is their most interesting point to the microscopist. This natural armour is in two parts which fit one within the other like the two halves of a Japanese basket. All manner of beautiful sculpturing marks these beautiful frustules as they are called; in some cases they are perforated and the living matter from within passes through the pores and forms a jelly-like covering for the little plant. We must make a point of collecting all the Diatoms we can find, for they are always interesting; moreover, they are easily preserved and made into permanent slides, for the little plants may be boiled in acid to destroy their living parts and the frustules will survive the boiling undamaged. One might wonder how such humble plants, surrounded as they are with flinty walls, could increase. They frequently do so in a simple manner. The living matter of which the plant is composed pushes the frustules apart and divides across the middle. The result of this event is the formation of two plants, each with a single frustule. In a very short time each plant grows a new frustule, but it is always much smaller than the one with which it started. The movements of some of the free swimming, that is to say non-attached Diatoms, are worthy of study. The scientific name of one kind, translated into everyday language, means little boats, and indeed they are well named for their beautiful aquatic manœuvres rival those of any ship. Somewhat similar in habit to the brown Diatoms are the green Desmids, but, whereas, the former also occur in the sea, the latter are all confined to fresh water. Sometimes Desmids are so numerous that they make the pond water as green as green-pea soup. It would be as impossible to describe all these plants as was the case with the Diatoms, but generally they may be recognised by the fact that they are composed of two similar halves, separated by more or less of a waist. Although some of the Desmids exhibit a certain amount of movement they are not active like the Diatoms.