There are countless animals of the sea we have not so much as mentioned, but the marine gardens contain plants so interesting and so totally unlike those which live upon land that we must devote a few pages to them also. CHAPTER XVI THE MICROSCOPE BY THE SEASIDE--PLANT LIFE The plant life of the sea side may be divided into two natural groups (i) of plants living on the shore near the sea and (ii) of plants living in the sea, for part of each day at least. The former group contains many plants of exactly the same kind as occur far inland, together with a few typically sea-side plants such as Thrift or Sea Pink. They are, however, one and all land plants. In this chapter we shall confine ourselves to the real sea plants, the seaweeds. Before we study any of these interesting plants under the microscope, it will be useful to learn a little about seaweeds in general, because they are so totally unlike land plants in every respect. They belong to the great plant division known as the _Algæ_, to which also belong the Diatoms, Desmids, _Volvox_, _Spirogyra_ and many of the other plants we mentioned in our chapter on Pond Life. So we see that, although all seaweeds are _Algæ_, not all _Algæ_ are seaweeds. They are higher in the scale of development than Fungi, to which Bacteria, Yeast, Mould, etc., belong, though they are not so highly developed as Ferns and not nearly so advanced as flowering plants. A very short acquaintance with _Algæ_ will show us that they are either green, brown or red. The green _Algæ_ are nearly all fresh water forms, though a few are to be found in the sea; on the other hand brown and red _Algæ_ are common in the sea and rare in fresh water. As we study our seaweeds on the shore, if we are really observant, we shall notice that they live in zones or belts according to their colour. There are exceptions to this rule but, in general, the green seaweeds dwell in situations where they are only covered by the sea at high tide; the red seaweeds are to be found mostly where they are always below water and, between the two, the brown seaweeds occur. In some parts, this colour scheme is very striking. Frequently red seaweeds may be found above high-water mark it is true, but in such cases they nearly always occur in rock pools and they are invariably sheltered by brown seaweeds.