First Period.
Plate CCLIV. Fig. 1. Represents the seed-lobes some what magnified, soon after becoming visible to the naked eye.
Fig. 2. The same highly magnified and reversed, to shew its under side, with the mould adhering to the cen tral fibrils.
Second Period. • Fig. 3. Represents the first frond evolving from the circular opening in the centre of the lobes, of the natural size. The circular opening is formed by the elevation merely of the central margin of the lobes, by the germi nating frond.
. Fig. 4. The seed-lobes reversed, to shew the true root.
Fig. 5. The lobes cut off to shew the tuberous swelling of the young stem, with the young frond and root germi nating from it.
Fig. 6. Shews the young plant with a second frond evol ving from the same part.
As to the difference asserted by Gmrtner to subsist be tween the vitellus and cotyledon, having examined this sup posed organ, and compared it with his own recorded cha racter, "quod non extra senzinis test= efferatur, aut in fo lium excrescat, sicuti cotyledones facere solent," Exe.1, we are enabled to correct the error of this generally accurate observer. These lobes, in ferns at least, so far from re maining within the testa of the seed, gradually expand, from an apparent point to the diameter, in general in stances, of above a quarter of an inch. This is not the only case in which it is to be regretted that Gartner should have confined his observations to the first period only of the germinating process ; during which, the peculiarities in the structure of the embryo al e seldom fully developed. If, therefore, mere terms, of which there are already too many, do not usurp the place of things, the seed-lobes of not only an analogy with, but in fact partake of, the essential properties of cotyledons, so far as these have been accurately defined. 1st, They constitute the body of their minute seeds. 2d, They include within their substance the other organs of the embryo, which they nou rish, and, under the necessary circumstances, finally deve lope. 3d, As in the dicotyledonous seeds, these other or gans germinate from a tuber situated in the centre of the lobes.
Yet notwithstanding this congruity with dico tyledonous plants, ferns, both in the structure of their em bryo and manner of germinating, possess characters clear ly distinguishing them from all other plants hitherto de scribed.
1st, In other dicotyledonous plants, the seed-lobes, at least such as rise to the surface, are afterwards farther elevated by the growth of the young stein ; but this can not happen in ferns, whose seed-lobes, less perfectly di vided, and, expanding horizontally only, attain their full growth before the development of the other parts of their embryo.
2d, In other dicotyledonous plants, on the contrary, the root immediately germinating, contributes towards the evolution of the other organs of the embryo, and recipro cally, even to the expansion of the cotyledons themselves; whereas in ferns, previous to the shooting of the true root, the seed-lobes are nourished by minute fibrils, invisible to the naked' eye, shooting from around the centre of the seed-lobes, and adhering to the soft mould in the crevices of moist rocks, where they frequently germinate. In this state, these plants, like the larv? of many insects, have no similarity whatever to their future form, and must have been generally mistaken for young Hepatica', which, both in appearance and manner of growth, they somewhat re semble.
3d, In the seed-lobes of dicotyledonous plants, the ves sels conveying the green juice towards the other organs of the embryo appear elegantly ramified, distinct from the deeper green of the cellular substance ; whereas in ferns, on the contrary, the lobes of the cotyledon, when examined by the microscope, seem to consist entirely of a network of deep green cellular substance, without the least vestige of ramified vessels.
By these peculiarities, then, the true ferns are charac terised with much more precision, than by the circinate' involution of their fronds ; a form of vernation which is common to them, with certain kindred tribes, such as the Botrychiaceee, Cycadacex, Lycopodiacece, and as we shall afterwards find.