Further than this the spore alone has no power to go, and the prothallium is not truly the germ of the future plant. True germs, needing fertilization, are produced upon it, and also the means whereby they can be fertilized. These can be distinguished only by use of the higher microscopic powers. If a portion of the prothallium is examined, it will be found studded with little bladders, containing round semi-transparent bodies of a greenish hue.
There may also be seen, though in fewer numbers, pellucid cells of an entirely different character, consisting apparently only of a fine membrane, forming an angular chamber, shaped in some instances like a lantern of extreme delicacy and elegance. From the top of this chamber a funnel-like shaft descends to a little germ which is situated at the bottom. This germ is the real original of the future plant, and the round bodies in their little cells, just before described, are the means whereby it is to be fertilized and receive energy to develope into the perfect fern.
But how can the needful contact between the germs and the fertilizing bodies be brought about? Observation and experiment supply a strange answer to this question.
The round bodies in the tiny bladders acquire a spiral or shell-like form when they become mature. If a drop of water is then placed in contact with the bladders, their contents will suddenly escape, retaining for a moment the coiled appearance, but quickly lengthening and partially unrolling.
By means of hairs with which they are furnished, and which at once commence a ceaseless jerking motion, they forthwith launch out into the water, and conduct themselves therein more like creatures endowed with conscious life than mere organs of a settled and sedate member of the vegetable kingdom.
These bodies, drawing near the germ-cells in the course of their travels through the, to them, vast ocean of the water-drop, have been seen arrested in their progress and passing down the funnel-shafts to the germs below—so fulfilling the purpose for which they were designed and their curious swimming powers were given.
The germs, so fertilized, become the underground stems of which I have yet to speak, putting forth roots and producing the tender, rolled-up buds which finally expand into the fronds whose grace and beauty we so much admire.
These germs, appearing on the prothallium or leaf-like expansion of the spore, are the true representatives of seeds, and the swimming bodies correspond to the pollen or fertilizing dust of flowers.
Thus we see that germs and means of fertilization are produced in the fern as truly as in higher plants, and that the simple agency whereby the one may reach and exert the needful action upon the other, is the dew-drop resting on the prothallium from which they are developed. Without the dew-drop or the rain-drop as a means of communication both must perish with their mission unfulfilled. This is, perhaps, one of the most singular instances ever to be found, of the mutual dependency of created things, or, to give different expression to the same idea, of the mode in which each link of the great network of existence is connected with every other.
Returning to the fern, whose "strange eventful history" we have traced so far,—the germ enlarges and becomes what is usually called the root, but is really an underground stem. The true roots are the little fibres—often black and wiry, looking more dead than alive—which descend from this.