Amongst the Wracks, of which there are a number of kinds, the methods of increase reach a higher stage. First of all let us describe the plants, so that we may know what to look for. They all belong to the group of brown _Algæ_. The “Channelled Wrack” is, when fully grown, about six inches long. It is much branched, often almost yellowish in colour and grows just below high-water mark. Along one side of the plant there is a moderately deep groove. Here we may note that the Wracks grow in zones from just below high water mark to low water mark. A little nearer the sea than the haunts of the Channelled Wrack, we shall find the Flat and Bladder Wracks. The former is but six inches or so in length, with flat, forked fronds, along the centres of which runs a single rib. The Bladder Wrack varies considerably in size. It may be smaller than either of the Wracks we have already mentioned or it may be two or three feet in length. It is the one seaweed familiar to everybody. Nearer to low tide mark we shall encounter the Knobbed Wrack, greenish brown in colour and often as much as six feet in length. It is so named because from the sides of its flat, leathery, strap-like fronds, there arise little stalked bladders. Right at, and often beyond, low tide mark there dwells the Notched Wrack; very similar to, though larger than, the Flat Wrack, from which it may easily be distinguished by the fact that the edges of its fronds are toothed, after the manner of a saw. It is obvious that the structure of any one of these Wracks is much more complicated than is the case with _Ectocarpus_. The latter Alga was composed of a number of cells, similar to one another in every respect except size. If we tease a stem or a frond of one of the Wracks upon a slide and examine the result of our efforts under the microscope we shall see that the cells which compose the Wrack are not by any means similar to one another. Those of us who have mastered the, by no means difficult, art of section cutting, should cut sections of stem and frond and compare them with sections of leaf and stem of some higher plant. The comparison will show us that, although the seaweed does not exhibit the complicated structure of a flowering plant, it has at least three kinds of different cells--an outer layer, a central structure and an intermediate layer.