VEGETABLE KINGDOM. 135 



1. Fucoids, or those related to the tough leathery sea-weeds along 

 coasts, which are called Fuci, some of which, among modern species, 

 grow to a great size, attaining a length even of hundreds of feet. 



2. Plants having calcareous secretions. Among these there are (1) 

 the delicate Corallines, which have generally a jointed stem, and are 

 only imperfectly calcareous ; (2) the Nullipores, which are often like 

 stony corals in form and hardness, making incrustations, and also 

 branching more or less perfectly : they differ from corals in having 

 no pores or cells, not even the pin-punctures of the Millepores ; (3) 

 Coccoliths, lenticular calcareous disks, usually convexo-concave, less 

 than a thousandth of an inch in diameter, occurring in many places 

 over the ocean's bottom, and also in shallow waters. Named from 

 kokkos, seed, and \lQos, stone. 



3. Plants having siliceous secretions. Microscopic, and mostly 

 unicellular plants. The Diatoms secrete a siliceous shell ; and they 

 grow so abundantly in some waters, fresh or salt, as to produce large 

 siliceous accumulations. A few of these siliceous species are figured 

 above, in Figs. 193 to 198. 



There are also microscopic species called Desmids, that consist of 

 one or a few greenish cells, and secrete little or no silica. They do 

 not contribute largely to rock-making, like the Diatoms, but are com- 

 mon as fossils in flint and other siliceous concretions. Some are fig- 

 ured on page 257, Fig. 484 A. 



The minute plants of the waters are sometimes called Protophytes. 



The Charce are other Cryptogamous plants, having large calcareous 

 secretions. They are delicate aquatic species, in some respects related 

 to the Mosses. The dried plant affords 30 per cent, of ash, 95 per 

 cent, of which is carbonate of lime. Consequently, when abundant, 

 they contribute calcareous material to the bottoms of ponds. 



