Midland Naturalist/Volume 01/Abnormal Ferns
Abnormal Ferns.[1]
By E. J. Lowe, Esq., F.R.S., &c.
The reproduction of ferns from spores is a study of much interest, and one worthy of mare general attention. The modus operandi is fraught with difficulties. The minute size of the infant ferns in their first growth is in itself dangerous, as any neglect will at once destroy the whole crop. The spores germinate as mere green points, imperceptible at first to the unassisted eye, and only rendered visible by the look of greenness from a number springing into life together. Spores of ferns differ from seeds of plants, inasmuch as they have n special organs; consisting merely of a homogeneous cellular mass. In seeds the young roots and the young shoots are present in the embryo, being developed from determinate points; whilst spores, on the contrary, consist merely of single vegetable cells, growing indifferently from any part of the surface.
These points of life, (germinant fronds,) as they continue to grow have a strong resemblance to Liverwort, (hence the term Marchantia-like.) They gradually increase in size, and, they de net become impregnated, will occasionally exceed half an inch in diameter.
The impregnation of the germinal frond does not seem to be capable of being accomplished without the action of strong light; indeed, grown in a somewhat dark corner the growth seems to be arrested before arriving at that particular stage of life. The following experiment will illustrate what is meant:—Three years ago a large Wardian case was prepared, and the surface of the soil scattered over with spores from a number of varieties of Scolopendrium vulgare, Lustrea filix-mas, Athyrium filix-fœmium, Polystichum angulare, and of Lastrea dilatata; each species being in a separate partition, This case was placed in a somewhat dark corner, under a plant stage. When the spores had been sewn about six months the whole surface soil was covered over (and had been for several weeks previously) with the vivid green of the young ferns. At this time a second case was prepared, not for spore sowing, but for transplanting, in patches, the germinal fronds from the first case. Small portions of this green mass were lifted on the point of a knife and planted in thick lines. The second case was then placed in a light part of a greenhouse, having a north aspect. Under these circumstances the transplanted patches very soon grew rapidly, (whilst those in the case from which they were taken had made little or no progress.) and in six months the second case was filled with a mass of fronds, yet no fronds appeared in the original case. A third ease was then prepared, and for the second time small portions were removed from the first case into the new one, and this also was placed in a well-lighted situation, having a north aspect. After being in this third case less than six months a large number of fronds appeared, whilst still no fronds appeared in the original case. A fourth case is now about to be planted from the same original stock, which, although still looking green and healthy, has no fronds developed, and, indeed, the germinal fronds it contains are still little more than mere points. Thus, for three years the growing spores in a darkened corner have remained all but dormant, whilst those transplanted from it have, in a situation of stronger light, a forest of fronds, varying between one inch and six inches in length, according as they have been selected from the second of third cases. This is mentioned as a very curious fact.
In reverting to the various stages of development from the spore on the frond to the fully-grown plant, most persons have observed what they choose to call seeds on the underside of the frond (though not always necessarily on the underside). They are not, as we have just said, real seeds, but spores, the first process towards the development of a fresh plant. It may be mentioned briefly that about the year 1840 Professor Nageli, of Zurich, announced that he had made the discovery that in the Marchantia-like germinal frond (i.e., whilst in the Liverwort-like condition) were to be seen the organs of reproduction; and in about the year 1845 Count Suminski, of Berlin, confirmed the existence of these so-called Antheridia, and also that two kinds of cells existed on the young germ frond, and that the male cells on bursting threw out spiral thread-like bodies, thickened at one end, and furnished with cilia about the thickened part, and these, from their activity, were called "Animalcules." The Count farther stated that he had seen one of these spirals landed in a female cell. Hofmeister has since then distinctly observed the terminal end of the new axis produced within the pistillidium, (or female cell,) and looked upon the globular cellule in its centre as itself the radiment of the stem, the embryo originating from a free cell produced within it. Mettenius observed a nucleus within the globular cellule. Mereklin then declared that the spiral filaments swarmed about the postillidium in numbers, and that he had seen them on rare occasions penetrate it. Professor Henfrey, about 1850, wrote an interesting article on this subject.
Spores, when they are sown, germinate, yet they need not necessarily produce the same form as the frond from which they are taken. In their caterpillar or Marchantia-form stage of life they are said, as before mentioned, to flower, to have male and female organs or cells, (more male than female cells) and these be it remembered are before there are any fronds, and it seems probable that it really depends upon how this impregnation is effected as to what kind of frond springs up from the germinal frond. The female organs are described as cells, and the male organs as spiral filaments which are tossed into the air, some of which, by landing in these cups, fertilise the plant in its caterpillar stage, and thus enable it to put on its butterfly-life or fronds.
Let an example be taken in the Lady Fern, where a number of varieties have been sown together. Now, if a spinal filament from the variety Vietariæ be tossed into one of these female cells, we may naturally expect the fronds when they do appear to be more or less cruciform, like those of the variety Vietariæ; whilst if this filament had been thrown from the var. miltifidum instead, the result would be quite a different plant, a multifid but not a cruciform frond, unless the female cup belonged to a cruciform variety, under which circumstances there would probably result a combination of the two forms. Hence the endless variety that are now to be seen in a good collection. When once an abnormal form has been obtained, it seems only necessary to get a pedigree, i.e., three or four generations, and it becomes almost impossible to raise a seedling of the original normal form; whilst without this abnormal blood it is equally almost impossible to raise any but normal forms.
As regards the various normal forms that species will assume, it is a singular fact that most of our British ferns put on appearances closely in imitation of each other, that the varieties oi each species have many characters in common, and that a certain law of form of variety seems to extend more or less through both British and exotic species. The usual forms running through nearly all our British ferns are those having the fronds crested, crisp, imibricated, confluent, multifid, acuminate, narrow, plumose, interrupted, depauperate, vanmose, and dwarf; and not only this, but we have the multiple of these, or the combining together of two or three characters in one frond, such us the narrow-crisped, the multifid-crisped, or the narrow-multifid as examples. In a wild state abnormal forms are found most commonly where, from various causes, ferns do not grow luxuriantly, i.e., grow under difficulties. When ferns flourish in a high degree, it is almost useless to hunt for abnormal forms.
It seems that spores gathered from one portion of an abnormal frond will produces different varieties from the of spores gathered from another portion of the same frond; so that if an accidental abnormal portion of a frond be fertile it is not impossible to reproduce from its spores plants having fronds in imitation of the accidental abnormal form.
The method adopted by the author of this paper in raising plants from spores is one that can he recommended. Having carefully prepared the soil, and then roasted or boiled it, in order to destroy all animal and vegetable life, it is placed in a Wardian case or pan, having a glass cover. The soil if roasted will require to be wetted with boiled or distilled water in order to be of a proper moistness. It is then pressed until there is a smooth surface, and after this sown with spores, which should not be covered with soil. All watering must be done from below, i.e., the pan placed in a saucer full of water, immersed about one-third of its depth, and this wet either be oiled or distilled water, to prevent a confervoid growth on the surface, which would kill the young fern germs, On the surface becoming green with growing ferns, transplant with the point of a knife into much larger pans; and this can be best done by making small indents in the surface, and placing in them small patches of the spores, and lightly pressing each with a finger, taking care to wipe the finger dry after every pressure, or the young plants will cling to it. To procure new varieties, spares are scraped off portions of a number of curious fronds or parts of fronds of the same species, and sewn thickly together; and the reason for sowing thickly is that the germinal fronds by being pressed closely together by each other become more or less vertical, a position thought to be more easily fertilised by the male organs falling more readily into the female cells than when in a more or less horizontal position, as they would be if sown very thinly. Nature does, to same extent, provide for this by curling the thickened edges; yet under those circumstances, with thin sowing, the male spiral is move likely to be one from the same individual, and would therefore more probably produce a form identical with the parent germ frond; whereas, if the spores of many forms he sown together the chances seem to he much more in favour of the fertilization by another variety being accomplished. After gathering the fronds for spores, it is better to place them in drying papers for a day or two, and then scrape off the spores and sow immediately. Freshly gathered spores germinate much more quickly than those that have been kept for a time.
It has been said, sow together only varieties of the same species, though occasionally, but very rarely, two species may be crossed and hybrid spores produced. Still, it is so difficult to cross species that we have at the most only a few examples to quote. These instances are probably,—first, Lastrea remota, a cross between Lastrea dilatata, and Lastrea filix-mas; second, Asplenium microdon, a cross between Asplenirum mavinum and Asplenium lanceolatum; and third, Asplenium Germanican a possible cross between Asplenium ruta-muraria and Asplenium septentrionale. The author has failed to raise spores from any of these, and is not aware of any one else succeeding, whilst in a wild state the two so-called parents appear always to be growing together where the third form is found.
There are plenty of good-looking spores on Lustrea remota, yet they will not germinate. For the last ten years several pans of spores from this form have been sown yearly without a single plant having been raised.
It has been also a question with the author as to whether some of the forms of species that only bear sterile fronds may not also be hybrid species. All the varieties of the species will reproduce the abnormal forms as prolificly as the normal ones, whilst a so-called hybrid species will not reproduce.
There are not only abnormal varieties of ferns, but the normal forms of different localities differ so that when the common forms of certain localities are gathered together they display in a marked degree the departure from one form.
In nature the progress of change in form is very slow, although in the forms of some plants a more rapid development in some localities can be observed: thus, nearly all the Harts tongue ferns at Westward Ho; on the Castle Rocks, Scarborough; and at Dawlish, are once or twice branched or crested. These changes. however, become much more rapid when under the most favourable circumstances, such as obtaining a pedigree and continuing it.
With regard to the origin of species, it is learnt from the doctrine of evolution, that all are the descendants of a comparatively few originally created simpler forms; this doctrine teaches, (I now quote Sir Joseph Hooker's admirable Botany):—1st. That the descendant of every plant departs more me or less in character from its parents. 2nd. That of these variations, some are better fitted than others. and even sometimes than their parent was, to survive in the area the plant inhabits. 3rd. That the conditions of the area are, like the individuals, variable. 4th. That the number of details previous to maturity amongst the descendants is enormously greater than that of survivors, and that those deaths are due to the conditions of the area not having suited them. 5th. That the descendants best fitted to thrive under the conditions of the area will be the survivors. 6th. That these variation will hence ultimately, in certain places, supplant the parent form; and 7th. That the differences between a species and a variety being one of degree only, the variations accumulated through successive generations will become specific, and these again by a like process generic, and so on.
No investigations demonstrate in a more striking manner the truth of this Darwinian theory than such as this paper briefly demonstrates. There is undoubtedly a mathematical law in the changes of form, and this fact proves that Dr. Darwin's discoveries have vastly advanced our knowledge of the laws of nature.
This work was published before January 1, 1930, and is in the public domain worldwide because the author died at least 100 years ago.
Public domainPublic domainfalsefalse
- ↑ Read before the Biological Section of the Birmingham Natural History and Microscopical Society, December 11th, 1877,