QQ RHODOSPERME^E. 



acece. Those in which this character prevails are considerably 

 diversified, according to the quantity and consistence of the 

 gelatine ; some being flaccid and slimy, others of a cartilagi- 

 nous or horny nature. In others there is no distinct arrange- 

 ment of the cells into filaments, but the frond consists of a 

 multitude of six- or twelve-sided cells homogeneously packed 

 together, and compressed into a membranous or fleshy sub- 

 stance. Such a structure is technically called cellular, in 

 contradistinction to the former, which is said to be filamentous. 

 In some cases all the cells of the frond contain colouring 

 matter ; in others, colour is confined either to the surface 

 cells or to a stratum of varying thickness beneath the surface. 

 In the latter cases the colourless cells contain either a granu- 

 lar matter or are wholly empty. So far for the internal 

 nature of the frond. Externally it is formed, sometimes into 

 twiggy bushes, sometimes into broad laminae ; and very 

 frequently both these characters are combined; the lower 

 part being cylindrical, the upper branches expanding at the 

 apex into flat phyllodia. Regularly formed leaves sometimes, 

 but rarely, make their appearance, as in Delesseria ; or in 

 the beautiful exotic genus Polyzonia, which has the stem and 

 branches of a Polysiphonia, the fruit of Dasya, and leaves 

 that resemble those of a Jungermannia. But the most 

 curious and beautiful varieties of form are found in certain 

 exotic genera, formed, on various systems, into pieces of net- 

 work, resembling fine lace, and, like that article, wrought in 

 divers elegant patterns. One of these lacy plants occurs in the 

 Mediterranean. It resembles a Callithamnion in structure, 

 but all its ramuli anastomose into a net-work, instead of form- 

 ing a branching stem. The seas of the tropics afford a much 

 more complex structure, with a central stem, round which is 

 coiled, in spiral order, a delicate lacy net; and Australia 

 gives us several genera in which the idea is further improved 

 upon. One (Thuretia) resembles the skeleton of an oak-leaf, 

 but, when seen under the microscope, is found to be much 

 more complex. Another (Claudea) exhibits the retiform 

 structure in its highest perfection ; for here each fibre of the 

 net-work is itself a little leaf, with its midrib and lamina, and 

 the net is formed by the growing together of these little 

 leaves, on a regular plan; the tip of one constantly uniting 

 itself to the rib of another. 



Several of this sub-class assimilate carbonate of lime in 

 large quantities, so that the frond becomes perfectly stony, 

 and not recognizable, except by its vegetable form, from 



