threads Oscillatoria, and Protococci, described in our first chapter, to which we refer our readers. Formerly these seaweeds yielded a rich harvest to the proprietors of coast-lands. They were collected in immense quantities, piled on the shore and burned, the result being a solid cake of ash. This ash was known as "Kelp," and consisted largely of carbonate of soda and salts of potash, which are largely used in the manufacture of soap. This "kelp" formed a source of considerable revenue to those who possessed lands on the coast, by the sale of it to the soap manufacturers. But modern researches in chemistry have shown that carbonate of soda can be more cheaply obtained from common salt, and so the kelp industry has dwindled to very small proportions, and the chief use to which the "harvest of the sea" is now put is in the manufacture of manure. But there is also another and a most important use to which seaweeds are put-that is, in the production of a valuable substance called Iodine. The discovery was made in the early part of this century by a soapmaker of Marseilles, named Courtois, who noticed a blue vapour arising from his vats during the rapid evaporation of the ley. This circumstance led to the discovery of iodine, which is now such an important substance in medicine and the arts. Certain species of seaweeds are also employed to feed sheep and cattle. But probably the greatest value of this class of plants consists in the fact that they form at once the home and the food of countless species of fish, molluscs, and crustaceans; and, further, without their presence and oxygenating effects the ocean would be uninhabitable. No living thing could exist within its bounds, and, instead of being the highway of the world's commerce, it would become unnavigable-in fact, it would be one gigantic cess-pool, the receptacle of the world's sewage. Instead of the breezes from its bosom bringing the health-giving iodine and ozone to mankind, it would poison the whole atmosphere with its fœtid emanations; and all along the coasts there would be desolation and death for miles. Think, then, of the importance of this tribe of plants, lowly as are their position in the botanists' classification. Even the minute confervæ and diatoms of our ponds and streams are of the utmost importance in purifying the waters and sustaining the great numbers of animals that subsist upon decaying substances. Though the lowliest of all forms of life, they are, nevertheless, indispensable to the higher forms; and for this reason alone they merit some attention from us who stand at the other end of the scale of organisation. APPENDIX. A TABLE OF THE CRYPTOGAMIA, Or IT It may be objected that in the foregoing pages there is no systematic treatment of the various groups of flowerless plants. This is intentional. We have briefly alluded to all the orders of cryptogams, but have entirely ignored the position of these orders in scientific classification. For instance, we have grouped together what are popularly known under the general term of Mosses, although some are widely separated from the others in classification. Our reason for doing so is the fact that this book is intended for the non-scientific reader. For the benefit of those who wish to ascertain the proper relation of these orders to each other, we append a table of the classification of these plants. |