Vegetable Teratology. Maxwell T. Masters

fusion), and that pressure will induce the coalition of organs primarily distinct.

      CHAPTER I.

       COHESION.

      Following Augustin Pyranius De Candolle, botanists have applied the term cohesion to the coalescence of parts of the same organ or of members of the same whorl; for instance, to the union of the sepals in a gamosepalous calyx, or of the petals in a gamopetalous corolla. It may arise either from a union between organs originally distinct, or more frequently from a want of separation between parts, which under general circumstances become divided during their development. Nothing is more common as a normal occurrence, while viewed as a teratological phenomenon it is also very frequent. For the purposes of convenience it admits of subdivision into those cases wherein the union takes place between the branches of the same plant, or between the margins of the same leaf-organ, or between those of different members of the same whorl.

      Cohesion between the axes of the same plant.—This cohesion may occur in various manners. Firstly. The branches of the main stem may become united one to the other. Secondly. Two or more stems become joined together. Thirdly. The branches become united to the stem; or, lastly, the roots may become fused one with another.

      Fig. 2—Cohesion of two branches in Dipsacus sylvestris.

The first of these is most commonly met with, doubtless owing to the number of the branches and the facilities for their union. An illustration of it is afforded by the figure (fig. 2), showing cohesion affecting the branches of a teazle (Dipsacus sylvestris). Union of the branches may be the result of an original cohesion of the buds, while in other cases the fusion does not take place until after development has proceeded to some extent. Of this latter kind illustrations are common where the branches are in close approximation; if the bark be removed by friction the two surfaces are very likely to become united (natural grafting). Such a union of the branches is very common in the ivy, the elder, the beech, and other plants. It may take place in various directions, lengthwise, obliquely, or transversely, according to circumstances. This mode of union belongs, perhaps, rather to the domain of pathology than of teratology. Some of the instances that have been recorded of very large trees, such as the chestnut of Mount Ætna, are really cases where fusion has taken place between several of the branches, or suckers, thrown out from the same original stem.[10] The same process of grafting occurs sometimes in the roots, as in Taxus baccata mentioned by Moquin, and also in the aerial roots of many of the tropical climbing plants, such as Clusia rosea, &c.

      Fig. 3.—Fasciation in Lettuce.

      Fasciation.—In the preceding instances of union between the branches, &c., the actual number of the fused parts is not increased; but if it happen that an unusual number of buds be formed in close apposition, so that they are liable to be compressed during their growth, union is very likely to take place, the more so from the softness of the young tissues. In this way it is probable that what is termed fasciation is brought about. This is one of the most common of all malformations, and seems to affect certain plants more frequently than others. In its simplest form it consists of a flat, ribbon-like expansion of the stem or branch; cylindrical below, the branches gradually lose their pristine form, and assume the flattened condition.

      Fig. 4.—Fasciation in Asparagus.

      Fig. 5.—Fasciated branch of Pinus Pinaster.

      Very generally the surface is striated by the prominence of the woody fibres which, running parallel for a time, converge or diverge at the summit according to the shape of the branch. If the rate of growth be equal, or nearly so, on both sides, the stem retains its straight direction, but it more generally happens that the growth on one side is more rapid and more vigorous than on the other, and hence arises that curvature of the fasciated branch so commonly met with, e.g. in the ash (Fraxinus), wherein it has been likened to a shepherd's crook. It is probable that almost any plant may present this change. It occurs alike in herbaceous and in woody plants, originating in the latter case while the branches are still soft. It may be remarked that, in the case of herbaceous plants, the fasciation always affects the principal stem, while, on the other hand, in the case of trees and shrubs the deformity occurs most frequently in the branches; thus, while in the former it may be said that the whole of the stem is more or less affected, in the latter it is rare to see more than one or two branches of the same tree thus deformed. It is a common thing for the fasciated branch to divide at the summit into a number of subdivisions. These latter may be deformed like the parent branch, or they may resume the ordinary aspect of the twigs.

      Fig. 6.—Fasciation and spiral torsion in the stem of Asparagus.

      Sometimes the flattened stem is destitute of buds, at other times, these organs are scattered irregularly over its surface or are crowded together in a sort of crest along the apex. When, as often happens, the deformity is accompanied with a twisting of the branch spirally, the buds may be placed irregularly, or in other cases along the free edge of the spiral curve. In a specimen of Bupleurum falcatum mentioned by Moquin the spiral arrangement of the leaves was replaced by a series of perfect whorls, each consisting of five, six, seven, or eight segments, and there was a flower-stalk in the axil of each leaf.

When flowers are borne on these fasciated stems they are generally altered in structure; sometimes the thalamus itself becomes more or less fasciated or flattened, and the different organs of the flower are arranged on an elliptical axis. A case of this nature is described by Schlechtendal ('Bot. Zeit.,' 1857, p. 880), in Cytisus nigricans, and M. Moquin-Tandon describes an instance in the vine in one flower of which sepals, petals, stamens, and ovary were abortive, while the receptacle was hypertrophied and fasciated, and bore on its surface a few adventitious buds.[11] The pedicels of Streptocarpus Rexii have also been observed in a fasciated state.[12]

It has been occasionally observed that the fasciated condition is hereditary; thus, Moquin relates that some seeds of a fasciated Cirsium reproduced the same condition in the seedlings,[13] while a similar tendency is inherited in the case of the cockscomb (Celosia).

      With reference to the nature of the deformity in question there is a difference of opinion; while most authors consider it to be due to the causes before mentioned, Moquin was of opinion that fasciation was due to a flattening of a single stem or branch. Linnæus, on the other hand, considered such stems to be the result of the formation of an unusual number of buds, the shoots resulting from which became coherent as growth proceeded:—"Fasciata dici solet planta cum plures caules connascuntur, ut unus ex plurimis instar fasciæ evadat et compressus" (Linn., 'Phil. Bot.,' 274). A similar opinion was held by J. D. Major in a singular book entitled 'De Plantâ, Monstrosa, Gottorpiensi,' Schleswig, 1665, wherein the stem of a Chrysanthemum is depicted in the fasciated condition.

      Fig. 7.—Fasciation in the scape of the Dandelion (Leontodon Taraxacum).

The striæ, which these stems almost invariably present, exhibit the lines of junction,