6 
OUR MARINE ALGiE. 
the criteria by which the species of a plant is determined. 
Fronds vary much in form and colour, and as their con¬ 
figuration, whether simple and entire, or branched, may be 
taken as an index to the genera, so the colour, whether red, 
olive-green, or sea-green, with their variety of shades, may 
serve as an indication of the sub-order to which they belong. 
It has also to be noticed that fronds vary in their mode of 
growth, commencing in some cases at the tip of the old frond, 
and in others at the base. In the filiform genera the branches 
are “ deciduous,” a fact that has to be remembered by the col¬ 
lector, as specimens of the same species present very different 
aspects at the different seasons of the year. In the larger 
plants of the olive series the fronds are furnished with an in¬ 
telligent provision in the shape of air-vessels, or bladders, 
which give buoyancy, enabling them to float on the surface of 
the water ; the bladder-wrack or popweed being a familiar ex¬ 
ample. But it is the cellular structure of the frond, as exam¬ 
ined under the microscope, which above all discriminates the 
genera and species, and the plants cannot be correctly 
determined without this aid. 
The cells present a variety of forms, as spherical, oval, 
cylindrical, oblong, quadrate, clavate, etc. ; they differ in 
every species, and even in plants of the same species. 
Examples come from Jersey in the genus Codium where there 
is only a single cell, but others are more or less complex in 
their cellular structure. The stem of these is composed of 
two or more series of cells; the axial, those which form the 
centre, and are arranged lengthwise, either bound closely 
together, or separated by layers of gelatine ; and those which 
form the periphery, at the surface, which are generally smaller 
and horizontal. When the cells of these series are all of 
equal length, they appear to be jointed, and the stem is said 
to be articulate; but when unequal the stem is called 
inarticulate. Good examples of the former we have in the 
Polysiphonias. 
(To be continued.) 
It is announced that Professor Owen has resigned his position as 
superintendent of the Natural History Department of the British 
Museum. Though the mania of the anti-vivisectionists has led them 
to entitle him “ an old humbug,” because he will not agree with the 
doctrines of these “peculiar people,” there is probably no scientific 
man in the whole world, outside such craze-mongers, who will not 
view with regret the announcement that increasing years render such 
a step necessary. Professor Owen’s great services to science have 
been gratefully and appreciatively recorded in “ Nature,” not long ago, 
in an article of the series on “ Our Scientific Worthies.” 
