class="pginternal" tag="{http://www.w3.org/1999/xhtml}a">The Hartstongue82

HOW TO KNOW THE
FERNS

CHAPTER I
THE FERNS AND THEIR ALLIES

In its lowest forms vegetable life is a very simple affair. The minute Algæ which clothe damp surfaces with a green film show few indeed of the characteristics with which we are familiar in the higher plants. Certainly they are green, proving that the tiny cells of which they are composed contain the wonderful colouring matter—chlorophyll, by means of which they are able to assimilate carbon from the carbonic acid of the air. There is, however, in these lowly plants no sign of a stem, a leaf, or a root. As we ascend in the scale of vegetable life we begin to get an increasing number of distinctive characters. In the case of the Mosses we have plants with distinct stems and leaves. But Mosses have no true roots, neither is there any vascular (woody) tissue in their composition. Mounting yet higher in the scale we come to a very important and interesting group of plants usually referred to as the Vascular Cryptogams. In this group are included the Ferns, the Horsetails, and the Club Mosses. In passing, it may be pointed out that the term Cryptogam is a name which was originally given to the flowerless plants by Linnæus to indicate that the plan of fertilization was hidden. The name is still retained, but it has lost its meaning in this sense, in that since the introduction of high-power microscopes it is not necessarily more difficult to study the fertilization of the non-flowering plants than it is to watch the process in the kinds which bear blossoms.

A small acquaintance with the Vascular Cryptogams will show us that they approach very closely to the flowering plants, or Phanerogams, as they are called, in their general features. It is true that in the cases of the Club Mosses and Horsetails the leaves are small or very poorly developed, but with the Ferns the foliage is often of an advanced type. All the Vascular Cryptogams, apart from a few insignificant exceptions, produce real roots; and, as the name implies, in a botanical sense, evidence woody tissue in their composition. Whilst the Club Mosses and Horsetails are comparatively humble plants, the Ferns have reached a remarkable development in the arboreal species. These, of course, grow into large trees which may be fifty or more feet in height, with thick woody trunks. Our common Male Fern not infrequently forms a short trunk-like stem if it is allowed to remain in an undisturbed state for a number of years. Not all the Ferns are large or even of moderate size; many of the Filmy Ferns are so minute that they are often taken for Mosses by those who do not know any better.

All the Vascular Cryptogams show an alternation of generation; that is, in the life history of each plant there is a sexual and an asexual individual. As is fully explained later, the plant which arises from the spore of the Vascular Cryptogam is quite an insignificant body known as the prothallus. This has a comparatively short existence in most cases. It is on the prothallus, however, that the sexual organs are produced, and after fertilization the plant as we know it arises. This individual is called the sporophyte. The plant is responsible for the spores which are produced in little cases called sporangia. These are borne straight on the leaves, and are produced without anything in the way of fertilization having taken place. As far as the Ferns are concerned, the spores are all of one kind, but in certain of the Club Mosses two kinds of spores are produced.

Apart from a few exceptions the Vascular Cryptogams are mostly perennial in habit. In many cases other means of reproduction are available than the agency of spores. It is believed that the Bracken Fern is rarely reproduced by its spores. The increase of this plant seems to be very effectively carried out by means of the strong growing underground stems which shoot about in all directions. The Horsetails commonly propagate themselves in the same way, and it is this which makes them so difficult to eradicate in the garden. In the case of many Ferns a common mode of increase is that of budding off new plants on the leaf. The well-known New Zealand species, Asplenium bulbiferum, produces little buds on its fronds; these grow into small plants, so that each leaf may be responsible for dozens of new individuals. An even more singular case is the so-called Walking Fern from North America (Scolopendrium rhizophyllum), which bears long, tapering leaves something like our Hartstongue. These bend over in such a way that their tips touch the ground; on the point of the frond a bud is developed. Roots go down into the soil from the point of the frond, leaves shoot upwards, and thus a new plant is born. In some species of Club Moss the increase of the plant by spore production is supplemented by a plan which involves the bearing of