CHAPTER XXV.

FERNS AND THEIR RELATIVES

=Perhaps there is no family of plants so easy to recognise as the ferns.= It is nearly always a simple matter to know whether or not a plant is a fern, for although there are hundreds of different kinds, they all have the family characters plainly marked.

We have not very many ferns growing commonly in England, for they generally require a moister air than is usual in this country. By far the commonest is the bracken, which grows in all parts of the country, and sometimes in very large masses (~see~ Plate I.). Some people separate the bracken fern from the others, and speak of “bracken” and “true ferns,” but this is not at all correct, for the bracken is just as much a true fern as the others, only as it is so much commoner, people are apt to value it less.

In some countries, particularly in the tropics, there are (as well as ferns like ours) very large ferns with tall, strong, upright stems, and crowns of large spreading leaves. Such ferns you can see in Plate III., and they are called tree ferns. Notice how thick the stem is, and how large the leaves are compared with it, while the trunk seems to be all rough and hairy, which is due to the jagged bases of the old leaves which have fallen away. Yet even the tree ferns are easily recognised as belonging to the fern family.

Let us examine ferns in order to find out what are the points about them which are specially characteristic for their family, and which help us to separate them from the other plants.

1. We find that ~the fern body is clearly marked out into roots, stem, and leaves, but there appear to be neither flowers nor cones~.

2. The stem and roots have definite “water-pipe” cells, as you can see if you examine a thin slice with your magnifying-glass, but there are never rings of wood formed year by year, as in the higher families. The stems are frequently short and stumpy, and often run underground. They are usually covered by the rough leaf-bases of old leaves and by dry scales.

3. The leaves are generally few in number, often only three or four, but they are highly compound, and are split up into very many side leaflets. They are generally thin and delicate. When they are young they are rolled up in the bud in a close coil (~see~ fig. 127), and as they unfold they bend back. This way of coiling up is quite a special character of ferns. The buds are generally covered with flaky, shining scales, which stick all over the young leaf-stalk.

4. ~You have never seen a fern with flowers or seeds~, yet there are always plenty of new ferns every year. How are the young ones formed? For a long time botanists did not know, so that people thought there was some magic about it, but now we know the whole story, and it is a very interesting one.

5. ~There are no seeds~, and

6. Therefore there are ~no seedlings to have cotyledons~.

You must have noticed little dark brown spots on the backs of some fern-leaves. It is in them that you must look for the beginning of the new fern plants. The little patches are at first hidden by green coverings, but when they are ripe these bend back, and expose the little brown clusters within. If you look at one of these ripe patches with a magnifying-glass, you may be able to see a number of little roundish boxes on stalks. Each of these contains a number of tiny “spores” (which are ~single cells~ with the power to grow), and when the spore-cases are ripe they open and shoot out the spores, as you may perhaps see if you look closely at a ripe patch when it is taken into warm, dry air.

These brown patches are not at all like flowers, but in some way they do the work of flowers, for they give rise to cells which can carry on the life of the fern to a second generation. The way in which they do it, however, is totally different from that of the seed, and is quite the most special character of the ferns and their relatives.

The spores grow slowly when they come on to moist earth, but as their development takes a long time, you had better get some from a gardener which have already grown. As the spore grows, the one cell composing it divides and divides again, until there is formed a little filmy heart-shaped green structure called a ~prothallium~ (~see~ fig. 129), which is not in the least like a fern plant, for it is not more than a quarter of an inch across. It has no stem or leaves, and is only a thin layer of green cells, with a few root-hairs on the under side. Two of the cells formed on this little structure then unite and begin to grow while still attached to it, and finally they grow into the form of a very small, simple fern plant (~see~ fig. 129). So that between the old fern plant and the little fern “sporeling” (for we cannot call it a seedling) we find a whole new structure, the prothallium, which is quite different from the usual fern plant. This curious alternation of fern,--prothallium,--fern, and then again prothallium, is what we call “alternation of generations,” and is very characteristic indeed of the fern tribe.

Some ferns take a short cut, and bear little ones directly on their leaves without any prothallium. You see this in the “Hundreds and Thousands” fern, where the old plant is sometimes covered over with little ones, which will grow if they are taken off and planted carefully.

Sometimes people are deceived by what is called the “flowering fern,” and expect that it will have flowers. In this fern we find that all the spore-cases grow together on a special leaf, which is so covered by them that it looks quite different from a usual one, and is called the flower, though it is not one. In all other ways the story of the spore building and growth is like that of usual ferns.

In our study of ferns, you see that they have many characters which are exceedingly different from either the flowering plants or pine-trees. In fact, they are so different that we require to add some new points to our list of characters for family divisions, which are:--

7. ~Instead of flowers there are little spore-cases, which contain a number of simple one-celled spores.~ These are generally found on leaves which are otherwise like the rest of the leaves of the plant.

8. ~Each spore grows out to form a small green structure, which differs from the parent, and which we call the prothallium.~

9. ~The new fern-plant grows at first attached to the prothallium~, but soon grows out beyond it, and is quite independent.

What we call “ferns” are not the only plants which belong to this big family, for the club-mosses and also the horsetails have almost the same arrangement for their building of new plants. Our character-points (7) (8) and (9) apply to them, even though the rest of their structures appear to be so different from the ferns. They are, therefore, put in the same big family with the ferns, though they have smaller classes for themselves apart from the true ferns.

Neither the ferns nor their near relatives are very important in the vegetation of to-day, but very long ago they were among the chief plants in the world, and grew to be as big as forest trees. Even then, however, they had almost the same way of forming spores that they have to-day, a fact which still marks them out as a family different from all the other families of plants.