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the three great divisions of the algæ, the rhodosperms or red-spored seaweeds are those of which the general public knows most and the marine botanist least. And the reason of this is very obvious. The green seaweeds are so simply constructed, and their tissues are so transparent, that their examination presents little difficulty even to the most inexperienced eye. In them the whole plant is but a repetition of any one of its component cells. We find in them scarcely a trace of that principle of division of labour, so common in plants a little higher in the scale of creation, by which different parts of the plant are modified and set apart for the performance of different functions, so that to one is assigned the office of nourishing the plant, to another that of producing seed. There is, as physiologists term it, no differentiation. We have, therefore, only to cut a fragment from any part of one of these plants and place it beneath the microscope, and so far as its structure is concerned we see at once all that is to be seen. But the case of the red seaweeds is very different. Here the fronds of the plant are often so opaque that little can be made out under the microscope without previous dissection, or the preparation of very thin sections. Again, the green seaweeds will grow almost anywhere; they will bear excess of light and deficiency of water, so that we can keep them for any length of time in our aquaria, and watch the changes which they undergo. We can even, as we have seen, keep a fragment of a plant growing in a single drop of water on a slip of glass, and observe with the microscope the method of its growth. In the same manner we can trace the development of the spores and zoospores, and learn how each becomes a plant. Thus the solution of the various problems presented by the green seaweeds is a matter of comparatively little difficulty, though even in their case many points still remain doubtful. But the red seaweeds are far less hardy, and far more susceptible of injury from unfavourable external circumstances. Few of them can be cultivated successfully, and fragments of plants detached for examination will not continue to grow. Nor have the attempts which have been made to raise the red seaweeds from their spores been in many instances attended with success, so that we can scarcely wonder that the true nature of the fructification of these plants is still a matter of dispute among marine botanists.

In most, probably in all, of the red seaweeds two kinds of fructification occur, called respectively spores and tetraspores. The tetraspores derive their name from a Greek word signifying four, and are thus termed from the very curious circumstance that they are always divided into four parts called sporules. They are generally oblong or spherical bodies, and the fourfold division always takes place on one of three different plans. Either the tetraspores are cut into quarters by two cuts at right angles to each other, just as we usually divide an apple or an orange, or they are divided by radiating lines drawn from the centre of the spherical body, or, finally, in the case of the oblong tetraspores, division is effected simply by three parallel cuts. The tetraspores are generally hidden in the substance of the frond, and are then only to be detected by careful examination with a lens. Sometimes, however, they are external, either naked and attached to the branches, or contained in pod-shaped cases termed stichidia. The spores are always contained in a more or less perfect case, differing in construction in different families, and called a favella, a coccidium, or a ceramidium. These different kinds of spore case are very important in the classification of the red seaweeds. The first is simply an external tubercle containing a globular mass of spores, the second is a similar body containing a tuft of spores attached to a central column, while the third is an oval or urn-shaped case open at the end and furnished with a tuft of pear-shaped spores. It is universally agreed among botanists that of these two kinds of fructification both cannot be regarded as true spores, and that one must be looked upon as gemmules or buds, but whether the spores or the tetraspores are the true fruit is still an open question. In addition to the spores and tetraspores there are found in some of the rhodosperms certain organs termed antheridia, which have been supposed to play some part in the fertilisation of the spores, and which are said by some observers to contain minute globules, having a power of spontaneous motion, like the zoospores of the green seaweeds. This, however, is denied by most authors. The antheridia may be easily seen in any of the common species of polysiphonia, in which they form rather long white cells, collected in great numbers at the ends of the branches.

It will be seen from what has been said, that the accurate study of the red seaweeds is by no means easy. The mere identification of specimens is often to the beginner a matter of no small difficulty; depending, as it does, on the shape and arrangement of the minute cells of which the frond is composed, the construction of the spore-cases, and the division and disposition of the tetraspores. But to this branch of knowledge there does exist a royal road. The fortunate possessor of “The Nature-printed Seaweeds,” may easily identify his specimens, without troubling his head about coccidia and favellidia, spores and tetraspores, or fatiguing his eyes over the microscope in making out the shape and arrangement of infinitesimal cells. Those to whom this work is an unattainable luxury, will find “Harvey’s Manual of British Marine Algæ,” a good guide. It is generally a matter of little difficulty to determine to which of the three great orders a given specimen belongs, since colour, as has before been observed, is here for the most part a safe guide. But though the members of the different orders agree thus remarkably in this respect, so that whenever we see a red seaweed we know at once that it possesses tetraspores, and is constructed on the model of one or other of the families into which the red seaweeds have been divided, and whenever we see a green or brown seaweed, we may safely predict the absence of both these qualities, yet this statement is true, so long only as we confine our attention to healthy plants, growing in a situation favourable to the development of the species to which they belong. For the colouring