’ 
A BRITISH MARINE ALG. 
membranaceous expansions. Their form, situation, and characteristic dis- 
tinctions, will be fully described in connection with the figures of species 
which will form the illustrations to these pages. 
There is one fact which makes the study of cryptogamic botany 
peculiarly interesting, and that is that a large portion of fossil vegetation 
is very intimately related to some of the nobler flowerless plants, and 
probably exhibits far grander and more highly organised individuals than 
any which at the present time are found in a living state. The celebrated 
Hugh Miller informs us that fossilized algze were not discovered until so 
recent a period as the year 1856, when some of the fucoids, or kelp-weeds, 
were detected in some ancient rocks in Shropshire. In the ancient Lower 
Silurians of Dumfriesshire, these rock weeds were so abundant that they 
have produced large tracts of anthracite coal several feet in thickness. 
The string-like plant known as Chorda filum, or popularly, “‘ dead mens’ 
lines,’’ had a Lower Silurian representative, known to the paleontologist 
as Palwochorda, or ancient rope. The well-known “Carrageen moss ”’ of 
the Irish had also a Lower Silurian prototype, and our Fuci or rock kelp- 
weeds were represented by Fucoides gracilis of the Lower Silurians of the 
Malverns ; in fact, the Thallogens of the earliest periods of vegetation 
appear to have resembled in their general characteristics the alge or sea- 
weeds of the present era. 
Were I to attempt to give a history of the various systematic arrange- 
ments by different authors, or of the steps by which we have arrived at our 
present knowledge of marine vegetation, I should certainly weary the. 
reader; therefore I will state at once, that the plan I shall adopt in these 
pages is based on the system of the late Professor Harvey, of Dublin, as 
recently revised by Professor Agardh, the celebrated Swedish algologist. 
These admirable botanists have distributed the alge into three large 
groups, which may be briefly described as follows: First, or simplest in 
point of structure, Chlorospermee, mostly grass-green, but varying occa- 
sionally to olive, purple, or other tints; Melanospermee, olive-green, 
sometimes inclining to yellow or brown-olive ; and Rhodospermee, rose-red, 
with every variety of pink, red, or brown-red tints, sometimes purple, but 
very rarely green. These three great sub-divisions are separated into 
orders, genera, and species. The Chlorosperms consist at present of six 
orders and twenty-three genera. The Melanosperms of six orders and 
thirty-five genera, and the Rhodosperms of thirteen orders and sixty-six 
genera. The name alga, which, as Dr. Harvey says, formerly included the 
lichens, is now limited to that large group of flowerless plants which con- 
stitute the characteristic vegetation of the waters, the marine division of 
which is now popularly termed seaweeds. 
Seaweeds may be characterised as cellular flowerless plants, living in or 
entirely under water, and deriving nourishment throughout their whole 
substance from the medium in which they vegetate. Roots, properly so 
called, they have none; the base of the plant, by which it is attached to 
the rocks or other substances, serving merely as a holdfast, to prevent the 
