SEA-WEEDS
| 1. Fucus nodosus | 3. Codium tomentosum |
| 2. Nitophyllum laceratum | 4. Padina pavonia |
| 5. Porphyra laciniata | |
The Ulvæ retain their colour perfectly when dried, and, with the exception of U. latissima, are of a mucilaginous nature, and adhere well to paper, but, unfortunately, the graceful wavy outline of the fronds is lost in pressed specimens.
The ‘true laver’ mentioned above, which is also popularly known as Sloke, is closely allied to Ulva, but may be distinguished from it by the colour of its membranous fronds, which vary from a light rose to a deep purple or violet, occasionally inclining to olive, but never green. Its scientific name is Porphyra laciniata (Plate VII.), and it differs from the majority of the chlorospermeæ in having dark-purple spores, which are arranged in groups of four in all parts of the frond. The fronds are very variable in form and size, being sometimes ribbon-like, and sometimes spreading into an irregular sheet of deeply-divided segments; and the remarkable variety of form and colour has led to a division into several species. These, however, merge into one another so gradually that the separation seems to be hardly necessary.
The same remark concerning the multiplicity of species applies to another allied genus called Enteromorpha, in which the fronds are green and tubular, and often more or less branched. In these the colour varies from a pale to a dark green, and the cells are arranged in such a manner as to give a reticulated appearance. The commonest and best-defined species are E. intestinalis, the tubular fronds of which are constricted at intervals in such a manner as to resemble the intestines of an animal, and E. compressa, with branched fronds of variable form and size. The former is common on all our coasts, and may even be found in rivers and ditches some distance from the sea. It thrives equally well in fresh and salt water, and appears to grow most luxuriantly in the brackish waters of tidal rivers. The latter species also thrives best in similar situations.
Coming now to the red-spored sea weeds (Rhodospermeæ), we have to deal with some of the most charming of the marine algæ that invariably attract the sea-side rambler, and provide many of the most delightful objects in the album of the young collector. Their brilliant colours, varying from a light red to dark purple and violet, are sufficient in themselves to render them popular with the collector, but in addition to this striking feature they are characterised by extreme elegance of form and delicacy of texture. They are to be found in most rock pools, from near high-water mark downwards, the smaller and more delicate forms adding much to the beauty of these miniature seas; but the largest and many of the prettiest species exist only at or beyond the lowest ebb of the tide, and hence the algologist, in quest of these beautiful plants, will find it necessary to work at the very lowest spring tides, with the occasional aid of a small boat drifted into the narrow channels among outlying rocks, and a long hook with which to haul up submerged specimens; and it will also be advisable to search the line of débris at high-water mark after stormy weather for rare weeds that may have been detached and washed ashore by the angry waves.
While engaged in the former of these employments—the searching of outlying rocks with the boat—and also when examining the outer rock pools which are disturbed by the waves that wash over their banks, the simple instrument known as the water-telescope will prove invaluable. Everyone must have noticed how difficult it is to observe objects in water, the surface of which is disturbed by the wind or some other cause; but the simple appliance named, consisting only of a long tube of metal, a few inches in diameter, and painted a dead black inside, will enable the observer to see all submerged objects with the greatest of ease when the water is itself clear. The principle of the water-telescope is as simple as its construction; for the tube, protecting the surface of the water within it from the disturbances outside, prevents the light from being refracted successively in different directions, while the dead-black surface of the interior prevents those internal reflections that would otherwise cause the vision to be indistinct.
A few hours spent with the rhodosperms at the sea-side will be sufficient to show not only the great variety of their form and colouring, but also that the same species may vary according to the position in which it grows. Most of the smaller forms are delicate and filamentous, but others have expanded fronds which are very leaf-like. The brightest colours are usually to be found at or beyond low-water mark, where the weeds are covered with a considerable height of water for hours together, and also in shady situations at higher levels, while some of the species that grow in the upper rock pools are often of such a deep colour, with so much admixture of brown, that they may be easily mistaken for the olive melanospores to be presently described.
Most of the rhodosperms are attached directly to the rocks, and the larger species have often a root-like disc by which they are very firmly held; but some of the smaller species grow attached to larger weeds, into the substance of which they frequently penetrate; and it is possible that these derive some amount of nourishment from the sap of their supporters. Some are of a recumbent nature, being attached to the rock throughout their whole length, while others are so incrusted with carbonate of lime which has been extracted from the water that they resemble corals rather than forms of vegetable life. Nearly all of them contain a bright-red colouring matter in addition to the chlorophyll by which they are enabled to feed on carbonic acid gas.