The Fruiting of the Fern

Teacher’s Story

“If we were required to know the position of the fruit-dots or the character of the indusium, nothing could be easier than to ascertain it; but if it is required that you be affected by ferns, that they amount to anything, signify anything to you, that they be another sacred scripture and revelation to you, help to redeem your life, this end is not so easily accomplished.”—Thoreau.

HE fern, like the butterfly, seems to have several this-world incarnations; and perhaps the most wonderful of these is the spore. Shake the dust out of the ripened fern and each particle, although too small for the naked eye to see, has within it the possibilities of developing a mass of graceful ferns. Each spore has an outside hard layer, and within this an atom of fern-substance; but it cannot be developed unless it falls into some warm, damp place favorable for its growth; it may have to wait many years before chance gives it this favorable condition, but it is strong and patient and retains its vital power for years. There are cases known where spores grew after twenty years of waiting. But what does this microscopic atom grow into? It develops into a tiny heart-shaped, leaflike structure which botanists call the prothallium; this has on its lower side little roots which reach down into the soil for nourishment; and on its upper surface are two kinds of pockets, one round and the other long. In the round pockets are developed bodies which may be compared to the pollen; and in the long pockets, bodies which may be compared to the ovules of flowering plants. In the case of ferns, water is necessary to float the pollen from the round pockets to the ovules in the long pockets. From a germ thus fertilized in one of the long pockets, a little green fern starts to grow, although it may be several years before it becomes a plant strong enough to send up fronds with spore-dots on them. To study the structure of the spore requires the highest powers of the microscope; and even the prothallium in most species is very small, varying from the size of a pin-head to that of a small pea, and it is therefore quite difficult to find. I found some once on a mossy log that bridged a stream, and I was never so triumphant over any other outdoor achievement. They may be found in damp places, in greenhouses, but the teacher will be very fortunate who is able to show her pupils this stage of the fern. The prothallium is a stage of the fern to be compared to the flower and seed combined in the higher plants; but this is difficult for young minds to comprehend. I like to tell the children that the fern, like a butterfly, has several stages: Beginning with the spore-bearing fern, we next have the spores, next the prothallium stage, and then the young fern. While in the other case we have first the egg, then the caterpillar, then the chrysalis, and then the butterfly. Looking at the ripe fruit-dots on the lower side of the fern leaf, we can easily see with a lens a mass of tiny globules; each one of these is a spore-case, or sporangium, (plural sporangia), and is fastened to the leaf by a stalk and has, almost encircling it, a jointed ring. (See figure on page 686).

When the spores are ripe, this ring straightens out and ruptures the globule, and out fly the spores. By scraping a little of the brown fuzz from a fruiting pinna of the Christmas fern upon a glass slide and placing a cover glass upon it, we find it very easy to examine through the microscope, and we are able thus to find the spore-cases in all stages, and to see the spores distinctly. The spore-cases may also be seen with a hand lens, the spores seeming then to be mere dust.

The different ways the ferns blanket their spore-cases is a delightful study, and one which the pupils enjoy very much. All of our common ferns except the careless little polypody thus protect their spores. Whether this blanket be circular, or horseshoe-shaped, or oblong, or in the form of pocket or cup, depends upon the genus to which the fern belongs. The little protecting blanket-membrane is called the indusium, and while its shape distinguishes the genus, the position in which it grows determines the species. I shall never forget my surprise and delight when, as a young girl, I visited the Philadelphia Centennial Exposition, and there in the great conservatories saw for the first time the tree-ferns of the tropics. One of these was labelled Dicksonia, and mystified, I asked the privilege of examining the fronds for fruiting organs. When lo! the indusium proved to be a little cup, borne at the base of the tooth of the pinnule, exactly like that of our boulder fern, which is also a Dicksonia. I had a sudden feeling that I must have fern friends all over the world.

The children are always interested in the way the maidenhair folds over the tips of her scallops to protect her spore nursery; and while many of our ferns have their fertile fronds very similar in form to the sterile ones, yet there are many common ferns with fertile fronds that look so different from the others, that one would not think they were originally of the same pattern; but although their pinnules are changed into cups, or spore-pockets, of various shapes, if they be examined carefully they will be seen to have the same general structure and the same divisions however much contracted, as have the large sterile fronds. The Osmundas, which include the interrupted, the cinnamon and the flowering ferns, are especially good for this part of the lesson. The sensitive fern, so common in damp places in open fields, is also an excellent illustration of this method of fruiting. While studying the ferns, the teacher should lay stress upon the fact that they represent the earliest and simplest forms of plants, that they reached the zenith of their growth in the Carboniferous age, and that, to a large extent, our coal is composed of them. It is interesting to think that the exquisite and intricate leaf patterns of the ferns should belong to a primitive type. Often when I have watched the forming by the frost, of the exquisite fernlike pictures on the window-pane, I have wondered if, after all, the first expression of the Creator did not find form in the most exquisite grace and beauty; and if perchance the first fishes, so fierce and terrible, did not mark the introduction of Satan.