INTRODUCTION. 9 
plant from being driven about and destroyed by the action of the waves ; but 
as no vessels of absorption have hitherto been discovered in the roots and 
stems, it is evident that seaweeds do not derive their nourishment from the 
substance to which they are attached, for indeed they are found growing 
luxuriantly alike on iron and floating timber, on rocks and shells, on the 
carapaces of crabs, and even upon each other, in the latter case without 
any detriment whatever to the species on which they are parasitic. The 
roots or holdfasts in some are a flattened or slightly conical disc, in others 
branching and clinging fibres, and in the Laminarie or oarweeds, especially 
as the plants advance in growth, a series of grasping processes are thrown 
down from the stem, which adhere so firmly to the rock that it is extremely 
difficult to detach them. 
The alge, or seaweeds, consist entirely of cellular tissue—little mem- 
branous sacs or cells of various forms, with walls of different degrees 
of tenacity. These minute cells are empty or filled with granular 
organised matter, which divides and developes new cells; these again 
divide and produce others, and thus by this cell splitting, branches 
and spreading fronds or leafy expansions are produced, each order of 
cell-division proceeding according to the 
laws of growth of its own species. The 
cellular tissue of which all seaweeds 
are composed presents several varieties. 
The most common form of cell is that of a 
cylinder, generally much longer in propor- 
tion to its breadth, and when such is the 
case the cells are attached end to end, 
forming threads or filaments, numbers of 
which, branched or otherwise, make up 
the frond by becoming firmly attached in 
bundles. Many of the simpler kinds of 
seaweeds are made up of threads or strings 
of cells, some of which are elaborately 
branched, others unbranched, yet through- 
Fig. 1, Filament of Confervatortuosa. out the whole plant the cells or joints are 
i Spore clothed with atite taht , invariably produced in the unbranched 
oo, or er : _ kinds from the tips of the cells of those 
vice -gsiieas From Porphyralaci- + eneath them, or from the upper side, as 
well as from the tips of the joints in the 
branching species. A portion of a filament of Conferva tortuosa (Fig. 1) 
and a branchlet of Cladophora Hutchinsie (Fig. 2) will illustrate the 
simple cellular or jointed structure of branched and unbranched filaments. 
Polygonal and other forms of cells are found in the leafy and membranous 
species, the particular forms being in most cases due to cell-pressure 
during growth, some adhering very closely together, and accommodating 
their forms to the spaces they have to fill, while in others the cells are set, 
as it were, within a transparent gelatine, each cell being completely sepa- 
