50 MASSACHUSETTS HORTICULTURAL SOCIETY. 



every body of water ; they have an indestructible coating of silica, 

 and form in such quantities as to make thick deposits. The city 

 of Richmond, Va., is built upon a bed of diatoms, eighteen feet 

 thick. The polishing powder of domestic use, known as Tripoli, 

 is composed entirely of the fossil remains of these plants. 



Algm grow in salt water and in fresh. They have both a very 

 simple and a very complicated mode of reproduction. Some 

 species are wholly microscopic, while others are the largest vege- 

 tables in the world ; one, a species of Microcystis, growing off the 

 California shore, would, if in the air instead of the water, tower 

 more than one hundred feet above the tallest Sequoia in the Cala- 

 veras grove. A single plant of another sea-weed, by its great 

 and branching growth, is sufficient to entirely obstruct navigation 

 in channels otherwise deep enough to float many of the largest 

 vessels. The Sargasso sea, so called, near the centre of the North 

 Atlantic Ocean, is 260,000 square miles in extent, and is covered 

 with but a single species of sea-weed. Many of the Algae are 

 very beautiful, but are not cultivated to any extent, except per- 

 haps in some of the European aquaria. 



Fungi are more numerous than the Algne in number of species, 

 but the plants are smaller, a majority of them being microscopic, 

 as for instance the wheat smut, potato rot, bread mould, etc. 

 Some of the larger species are cultivated for the table, one of 

 which has been exhibited in this room. Fungi are very compli- 

 cated in their reproduction, and grow with great rapidity, but 

 are credited with a more rapid growth in many instances than 

 is due them, as the root-like mycelium may have been growing 

 a long time unobserved before the fruiting portion, the only part 

 generally noticed, makes its appearance. 



Lichens are now the subject of a botanical dispute ; they grow 

 upon wood and rocks, and are used only in cultivation as an orna- 

 ment to the fernery. 



Mosses and Hepaticcv. are also familiar objects. Single speci- 

 mens of the mosses are very minute, yet b}'^ their vast quantity 

 the}' cover ofiten an extended area, contributing a beautiful effect 

 to the fernery or grotto, and are in nature a most pleasing object. 

 They are also invaluable to the florist for various economic pur- 

 poses. 



Of the Lycopods the genus Selaginella is the only one much 

 cultivated. The allied genera Lycojiodium and Selaginella have 



