The best known of the green-spored weeds are certainly those belonging to the _Ulvaceæ_, characterised by their flat or tubular fronds, sometimes of a purplish colour, the cells of which multiply both horizontally and vertically as the plants grow. In the typical genus, _Ulva_, the frond is sometimes in two distinct layers, and becomes more or less inflated by the accumulation of either water or oxygen between them. The commonest species are _U. lactuca_ and _U. latissima_, both of which are eaten by the dwellers on some of our coasts. The former, commonly known as the Lettuce Ulva, has a frond of a single layer of cells, and grows on rocks and weeds between the tide-marks. It is common on many oyster beds, and is employed by the fishermen to cover the oysters when sent to market; they call it ‘oyster green.’ This species is shown on Plate VIII. _U. latissima_ or the Broad Ulva sometimes reaches a length of two feet, and a breadth of nearly a foot. The fronds are composed of two layers of cells, are of an irregular shape, with a very wavy, broken margin, and of a bluish-green colour, It is known as the Green Laver, and is used as food in districts where the true laver (_Porphyra_) is not to be obtained. A third species--the Narrow Ulva (_U. Linza_)--has smaller and narrower fronds, of a more regular shape and of a bright-green colour. The fronds are composed of two layers of cells. [Illustration: Plate VII. SEA-WEEDS 1. Fucus nodosus 2. Nitophyllum laceratum 3. Codium tomentosum 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.