MELANOSPERME.E. 9 



existence : but the majority which grow on other species are 

 merely epiphytes, many of them indifferently growing on 

 living plants or on dead substances. Several are minute, 

 but very few of strictly microscopic size. Almost all have a 

 distinction, in their vegetation, of root, stem and branches, 

 and many possess well formed, and even nerved leaves. In 

 a very few, the frond is a shapeless mass, or a crust lying 

 close on the surface of rocks. None deposit carbonate of 

 lime in their tissues, but most, perhaps all of them, yield 

 iodine, and are the chief source from which that valuable 

 substance is obtained. 



In the fructification of these plants there is considerable 

 uniformity in the structure and origin of the spores, while 

 there is a great diversity in the position and grouping together 

 of those bodies, and in the supplementary organs which ac- 

 company them. The spores are always formed from a single 

 cell, within which, as it enlarges, a dense, olive-coloured, granu- 

 lar substance gradually accumulates and acquires consistence. 

 In some this internal matter, or endochrome, forms at matu- 

 rity a single compact mass, giving birth, on germination, to 

 a single plant ; but in others it is parted into two, four, or 

 even eight sporules (as in Fucm and Cutleria), each of 

 which is the germ of a new individual. It is manifest there- 

 fore that the spore is the representative rather of a seed-ves- 

 sel, usually one-seeded, but sometimes many-seeded, than of 

 the seed itself: and therefore. the term utricle, applied by 

 some botanists to this body, is more consistent with organi- 

 zation. In the simplest individuals of the sub-class the 

 spore is formed out of one of the surface cells, which rises 

 above its fellows, and is either altogether naked, or accom- 

 panied by a few jointed threads, to which the name parane- 

 mata is given. In the Dictyotacea, in which family the 

 spores are distributed over the surface, the paranemata are 

 in general little developed, consisting, as in Punctaria and 

 Asperococcus, of a few short, confervoid filaments ; but in 

 Slilophora, a more compound genus of the same group, they 

 form the principal portion of the masses of fructification, and 

 are considerably organized. In Chordaria and Mesoyloia 

 the whole outer coating of the frond is composed of these 

 organs. It is among the FUCACE.E, however, that we find 

 them in their highest form ; and here there is a manifest 

 separation of the organ into two parts ; the jointed filament 

 simple or branched and the antheridia, little transparent 

 cells full of orange-coloured moving particles, borne by the 



