"We have the receipt of fern-seed We walk invisible".
- King Henry the Fourth.
WHEN Falstaff, of delightsome - though not of blessed - memory, had perpetrated a number of lawless deeds, without either fear or reproach, he boasted that he and his cronies "had the receipt of fern-seed".
The fine dust which borders the matured fronds of the common bracken was supposed to confer magic powers upon whomsoever should gather it with proper ceremonies, at the stroke of twelve, on midsummer's night. Chief of these, and most useful to gentlemen like Falstaff, with great appetites and slender purses, was the power of becoming invisible at will.
The experience of four more centuries has taught us that uncriticised appropriation of other men's goods comes never by aid of fern-seed, and only sometimes by bribing or hoodwinking the powers that be.
And modern science tells us that there is no such thing as fern-seed, for the tiny globular or oval bodies from which flowerless plants are perpetuated are not seeds, but spores.
The seed, as we have seen, consists generally of two coats, enclosing a tiny plant and a store of food for its sustenance during the first few days of its life above ground.
But the spore is much simpler in structure. Its morphological equivalent in the flowering-plant is not the ovary, nor even the ovule or young seed within the ovary, but it is a tiny vesicle or cell which formed inside the ovule when the flower first unfolded.
In the flowering-plant the jelly-like substance of this cell mingles with some of the jelly in the pollen-grain, and after this union is complete the cell begins to grow and shape itself into a tiny plant. This union of the contents of the pollen-grain with the vesicle in the ovule has been understood, though less fully than we understand it to-day, for two centuries or more. Hence, all the plants which bear flowers with stamens and pistils, and so have ovules and pollen, are called "phanerogams," the term being derived from two Greek words which mean a visible or apparent marriage.
It was long suspected that among flowerless plants also the new individual was born as the result of the union of two parent-cells, but with the imperfect microscopes of former times this union could not be seen in detail, and the facts concerning it could never be accurately learned.
So all the series of the flowerless plants, among which are numbered lichens, seaweeds, mosses, liverworts, horsetails, and ferns, were named "cryptogams," from two Greek terms, which mean a hidden marriage.
But little is hidden by mere minuceness from the modern compound-microscope, and though some of the smallest cryptogams - the microbes and bacteria - have "ways that are dark" still, the life-history of the mosses, liverworts, horsetails, and ferns is now accurately known.
The differences between these two great series of plants - the flowering and the flowerless - are sharply defined at the very beginning of their histories. In the ripe seed the little plant is already formed.
It lies snugly folded into the smallest possible compass, and is very pale and tiny, but even a pocket-lens will show that it has a leaf, or two, as the case may be, a little stem, and at the end of this a knob, whence the first roots will spring.
And this little plant, in due time, will grow into the exact likeness of the parent-plant from which it sprang.
Judged by their exteriors, the little spores which dust the edges or dot the backs of fern-leaves are more elaborate than seeds, for the fern-spore has always two coats, and sometimes three, and the outermost coat is often as daintily wrought as if a fairy carver had expended his best skill upon it. But inside careful investigation with the most powerful of microscopes finds only a minute drop of jelly, containing a little starch, some oil, and many tiny floating grains of chlorophyll. No germ is contained within the spore of any cryptogam.
But the jelly, or protoplasm, in the spore is instinct with creative life. When growth begins, the outer coat of the spore breaks irregularly, and the inner coat, with part of its contents3 protrudes through the fissure, forming a knob, which is soon cut off from the rest of the spore by a transverse wall. This outgrowth contains little or no chlorophyll, and it lengthens rapidly, plunges downward into the soil, and serves all the purposes of the first rootlet in the sprouting seed-plant.
Meantime the larger and greener portion of the spore stretches out into a tube, and a little later partitions grow across the interior of this tube, cutting it up into a chain of cells. Later still the cell at the outermost end divides into two by a lengthwise partition. Then all the cells begin to divide lengthwise and crosswise by the growth of delicate walls within them, till there is formed a sheet or plate of tissue, with the general outline of a flattened heart. Toward the centre of this heart, on the side which lies undermost, rows of new cells are now produced by the growing and splitting of old ones, till a cushion of tissue is formed.
And the under surface of the little heart also gives rise to a number of long, slender tubes, as fine as hairs, which are called "root-hairs," because their office is the same as that of the roots of higher plants (Fig. 68).
They anchor the little heart to the spot where it grew, and they help to sustain its life by absorbing moisture from the soil.
The mass of cellular tissue resulting from the development of the spore is called a prothallium, or prothallus.
The adders'-tongues, next of kin to the ferns and the horsetails, or scouring-rushes, both shed spores, which develop into prothalli. So do the lycopodiums, which, under the names of "ground-pine," "club-moss," or "trailing-evergreen," are familiar to almost every one who has summered in New England.
Fig. 68. - Prothallus of a southern fern (Pteris serrulata). a, actual size; b, much magnified.