SEPARATION OF MIXED CHARACTERS (FERNS)
Chas. T. Druery, F.L.S., V.M.H.
IN the offspring of hybrid plants, the phenomenon of dissociation of characters which were combined in their parents is common enough, and is due to reversion, the reproductive gemmules sorting themselves out as it were in the pollen grains and ovaries according to certain laws, which seem to determine the results on definite lines to judge by, at any rate, Mendel's experiments. There are, however, dimorphic plants which cannot be imputed to hybridisation, or even varietal crossing, and which nevertheless must, adopting the pangenetic hypothesis of Darwin, be pervaded with gemmules of two classes, as distinct from each other in their constructive faculties, as those of two quite different species. A marked example of this kind exists in a varietal form of Scolopendrium vulgare, found many years ago near Falmouth by Miss Drummond, and hence named S. v. crispum Drummondiae. The non-hybrid character of this Fern is established at once by the solitary character of the species in Great Britain, and that it is not a natural cross between two varieties we must assume from the fact that varieties are numerically excessively rare, and that the marked peculiarities of this particular type are not known to exist as separate types at all.
This Fern is practically unique as an example of complex variation, the normal flat strap-shaped frond of the species being dimorphically transformed into two types, one with smooth-edged fronds, extra long and narrow, and having a very broad, flat ramo-digitate crest at the top, sometimes 9 inches across; the fronds, moreover, are undulate in the plane of the lamina, the rachis curving repeatedly switchback-fashion. The fronds are fertile, bearing short sori at intervals. The second type of frond is similar as regards the features described, but has all the edges deeply fimbriate, and cut into long slender segments, the points of which are aposporous, producing prothalli freely when severed and layered, and such prothalli yielding plants in the normal sexual manner.
Prior to the discovery by the writer of the aposporous character of the fimbriate fronds, which are mixed with the smooth-edged ones quite indiscriminately, a number of plants were raised from the spores, and among these offspring the faculty of dissociation of the two characters asserted itself, since a number of these proved entirely and constantly fimbriate, the smooth-edged fronds being apparently quite eliminated. A very fine specimen of this class, bearing dense corymbose fringed tassels, instead of flat, digitate ones, and with the fimbriation greatly enhanced, was brought to the writer's notice two years ago by the raiser, Mr. H. Batten, of Warton, near Carnforth, who very kindly gave me a portion of a fringed crest, and also with a view to obtaining a perfectly true specimen, a base of one of the old fronds, i.e., the fleshy permanent portion immediately attached to the caudex. The fringed crest being layered, produced in due course a mass of prothalli and young plants, more of which promise to be fair reproductions of the fringed type; but one has thrown up several fronds all smooth-edged, though otherwise typical of the variety. The most unexpected development, however, arose from the frond-base. These bases, as is now well known, if severed, and even if cut through into two, and inserted in soil, or dropped into a tumbler with a little wet sand at the bottom, and kept close, develop in the course of a few months small excrescences apparently from any point, including the cut surfaces themselves. These excrescences are buds, and frequently a single base in this way may yield a cluster of youngsters, usually typical. In this case, however, only two such buds were formed, one on each side of the basal piece; and to my great surprise, as these two developed, they presented another example of dissociation, one being quite devoid of fimbriation, though frilled and crested, while the other was an extreme type of the aposporous character, the fronds so far being attenuate, with deeper out basal lobes, and stiff, radiating, fimbriate crests, altogether different indeed from its immediate neighbour developed from the same base, fashioned from the same sap, and originating under identical circumstances from the outset. Here, it will be seen, the parent had thrown off the plain-edged character entirely, though derived from a spore of a dimorphic form, and yet retains within it the dimorphic faculty to a sufficient extent, not only to yield two kinds of plants through its aposporous fringes, but independently of sexual action, to do the same thing by asexual buds abnormally induced from the severed frond bases. The two types of frond do not appear to be indeterminate at all: they are never half and half or intermediate in any way, hence we have the curious phenomenon that the primary cells which initiate the formation of a frond, have, as it were, at the outset two different architectural plans to select from; but what law determines their selection is part of that great puzzle which variation still constitutes for all investigators.