we may often come across it in our rambles if we take the trouble to use our eyes. There are other extremely beautiful forms of fresh-water algae. Here in this same stream are the long green threads of _Cladophora glomerata_. I use as few hard words as possible, but I cannot help using them sometimes, as many objects have no English names. This alga is also attached to stones and floats out with the current sometimes two feet in length; and, like the frog-spawn alga, is fond of pure water, but I have often kept the _Cladophora_ alive in perfect health in an aquarium for weeks together. Its deep refreshing green colour and graceful form make it a very desirable acquisition for the aquarium. I break off a small bit. Now see its beautifully branched form. Do you remember a round green ball about the size of a small apple which I have at home? Well, that ball, which came from Ellesmere, is nothing else than a mass of this same _Cladophora_. Dr. Hassall is no doubt correct in his explanation of the formation of these balls. He says, "This state of _Cladophora glomerata_ I believe to be formed as follows: A specimen by the force of some mountain stream swollen by recent rains becomes forced from its attachment; as it is carried along by the current, it is made to revolve repeatedly upon itself, until at last a compact ball is formed of it, which finally becomes deposited in some basin or reservoir in which the stream loses itself, and in which these balls are usually found." Here are some specimens in the water of a rich brown colour instead of green. This is caused by the growth of other algae over its long branches. See! I shake a bit in my bottle, and you see a quantity of brown deposit comes off, showing the green threads of the _Cladophora_ underneath. This brown deposit looks to you, I dare say, very uninteresting. I will show you some under the microscope when we get home, and you will see many extremely beautiful forms. These are known by the name of _Diatomaceae_ and _Desmidiae_. I will not tell you more of them at present; but a picture which I will show you will give you the forms of some of these microscopic plants. [Illustration: FRESH-WATER ALGAE, DESMIDEAE, AND DIATOMACEAE. All highly magnified. 1.--Staurastrum. 2.--Trigonocystis. 3.--Euastrum. 4.--Closterium. 5.--Diatoma. 6, 7.--Meridion. 8.--Eunotia. 9.--Exilaria.]