Chapter 26

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.

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.

=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.

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.

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.

The striæ, which these stems almost invariably present, exhibit the lines of junction, and the spiral or other curvatures and contraction, which are so often met with, may be accounted for by the unequal growth of one portion of the stem as contrasted with that of another. Against this view Moquin cites the instances of one-stemmed plants, such as _Androsace maxima_, but, on the other hand, those herbaceous plants having usually but a single stem not unfrequently produce several which may remain distinct, but not uncommonly become united together. Prof. Hincks[14] cites cases of this kind in _Primula vulgaris_, _Hieracium aureum_, and _Ranunculus bulbosus_. I have myself met with several cases of the kind in _Primula veris_, in the Polyanthus, in the Daisy, and in the _Leontodon Taraxacum_, in which latter a fusion of two or more flower-stems bearing at the top a composite flower, and made up of two, three, four, or more flowers combined together, and containing all the organs that would be present in the same flowers if separate, is very common.

Moquin's second objection is founded upon the fact that, in certain fasciated stems, the branches are not increased in number or altered in arrangement from what is usual; but however true this may be in particular cases, it is quite certain that in the majority of instances a large increase in the number of leaves and buds is a prominent characteristic of fasciated stems.

Another argument used by the distinguished French botanist to show that fasciated stems are not due to cohesion of two or more stems, is founded on the fact that a transverse section of a fasciated stem generally shows an elliptical outline with but a single central canal. On the other hand, if two branches become united and a transverse section be made, the form of the cut surface would be more or less like that of the figure 8[Symbol: 8 turned 90°], although in old stems this may give place to an elliptical outline, but even then traces of two medullary canals may be found. This argument is very deceptive, for the appearance of the transverse section must depend, not only on the intimacy of their union, but also on the internal structure of the stems themselves. When two flowers cohere without much pressure they exhibit uniting circles somewhat resembling the figure of 8[Symbol: 8 turned 90°], but when more completely combined they have an outline of a very elongated figure, and something similar is to be expected in herbaceous stems. Even the elongated pith of a transversely cut, woody, fasciated stem only marks the intimate union of several branches, and Prof. Hincks, whose views the writer entirely shares, has noticed instances of the union of two, and of only two, stems where the internal appearance was the same as in other fasciations.

Moquin, moreover, raises the objection that it is unlikely that several branches should become united lengthwise in one plane only, and, further, that in the greater number of fasciations all the other branches which should be present are to be found--not one is wanting, not one has disappeared, as might have been anticipated had fusion taken place. In raising this objection, Moquin seems not sufficiently to have considered the circumstance that the buds in these cases are in one plane from the first, and are all about equal in point of age and size.

The last objection that Moquin raises to the opinion that fasciation is the result of a grafting process is, that in such a case, examples should be found wherein the branches are incompletely fused, and where on a transverse section traces of the medullary canals belonging to each branch should be visible. The arrangement of leaves or buds on the surface should also in such a case indicate a fusion of several spiral cycles or whorls. To this it may be replied that such cases are met with very frequently indeed. A figure is given by De Candolle[15] of a stem of _Spartium junceum_ having several branches only imperfectly fasciated.

Fasciated stems, then, seem to be best explained, as is stated by Prof. Hincks, "on the principle of adhesion arising in cases where from superabundant nourishment, especially if accompanied by some check or injury, numerous buds have been produced in close proximity, and the supposition that these growths are produced by the dilatation of a single stem is founded on a false analogy between fasciated stems and certain other anomalous growths."

It will not, of course, be forgotten that this fasciated condition occurs so frequently in some plants as almost to constitute their natural state, _e.g._ _Sedum cristatum_, _Celosia_, &c. This condition may be induced by the art of the gardener--"_Fit idem arte, si plures caules enascentes cogantur penetrare coarctatum spatium et parturiri tanquam ex angusto utero, sic sæpe in Ranunculo, Beta, Asparago, Hesperide Pinu, Celosiâ, Tragopogone, Scorzonerâ Cotula foetida_," Linnæus op. cit.

Plot, in his 'History of Oxfordshire,' considers fasciation to arise from the ascent of too much nourishment for one stalk and not enough for two, "which accident of plants," says Plot, the German virtuosi ('Misc. Curios. Med. Physic. Acad. Nat. Cur.,' Ann. i, Observ. 102,) "think only to happen after hard and late winters, by reason whereof, indeed, the sap, being restrained somewhat longer than ordinary, upon sudden thaws may probably be sent up more forcibly, and so produce these fasciated stalks, whereas the natural and graduated ascent would have produced them but single." Prof. Hincks' explanation is, however, more near to the truth, and his opinion is borne out by the frequency with which this change is met with in certain plants which are frequently forced on during their growth, as lettuce, asparagus, endive, &c., all of which are very subject to this change. In the 'Transactions of the Horticultural Society of London,' vol. iv, p. 321, Mr. Knight gives an account of the cultivation of the cockscomb, so as to ensure the production of the very large flower-stalks for which this plant is admired. The principal points in the culture were the application of a large quantity of stimulating manure and the maintenance of a high temperature. One of them so grown measured eighteen inches in width.

The list which is appended is intended to show those plants in which fasciation has been most frequently observed. It makes no pretension to be complete, but is sufficiently so for the purpose indicated: the * denotes the especial frequency of the change in question; the ! indicates that the writer has himself seen the plant, so marked, affected in this way. The remainder have been copied from various sources.

EXOGENS.

[Greek: alpha]. _Herbaceous._

Ranunculus tripartitus. * bulbosus! Philonotis. Delphinium elatum. * sp.! Hesperis matronalis. *Cheiranthus Cheiri! *Matthiola incana! *Brassica oleracea! var. pl. inflor. Linum usitatissimum! Althæa rosea! Lavatera trimestris. Geranii sp. Tropæolum majus! Viola odorata inflor.! Reseda odorata! Fragaria vesca. Ervum lens. Trifolium resupinatum. repens! pratense! Saxifraga mutata. irrigua. Bupleurum falcatum. Bunium flexuosum. *Sedum reflexum! cristatum! Epilobium augustifolium! Momordica Elaterium! Gaura biennis. Cotula foetida. Barkhausia taraxacifolia. Carlina vulgaris! Apargia autumnalis. *Leontodon Taraxacum inflor.! Centaurea Scabiosa. *Cichorium Intybus! Hieracium Pilosella. aureum. umbellatum. *Chrysanthemum Leucanthemum. indicum! Anthemis nobilis. arvensis. Cirsium lanceolatum. Conyza squarrosa! Inula dysenterica! Tragopogon porrifolium. Cnicus palustris. Carduus arvensis! Helianthus tuberosus! annuus. Cineraria palustris. Helianthus sp.! Dahlia variabilis. Bellis perennis inflor.! Coreopsis sp.! Crepis virens. Lactuca sativa! Zinnia elegans. *Campanula medium! rapunculoides. thyrsoidea. Dipsacus pilosus. fullonum. silvestris. Knautia arvensis. Phyteuma orbiculare. Jasione montana. *Linaria purpurea! Antirrhinum majus! Veronica amethystea. Veronica maritima. sp. Russellia juncea! Digitalis purpurea! Ajuga pyramidalis. Hyssopus officinalis. Dracocephalum moldavicum. Myosotis scorpioides. Echium pyrenaicum. simplex. Stapeliæ sp. Lysimachia vulgaris! Androsace maxima. Primula veris inflor.! denticulata inflor.! Polemonium coeruleum. Convolvulus sepium! arvensis! Plantago media. *Euphorbia Characias. exigua. * Cyparissias. Suæda maritima. *Celosia sp. Beta vulgaris inflor.! Phytolacca sp.

[Greek: beta]. _Woody._

Berberis vulgaris. Hibiscus syriacus! Acer pseudo-platanus! Dodonæa viscosa. Sterculia platanifolia. Euonymus japonicus! Vitis vinifera inflor.! Spartium Scoparium! Spartium junceum! Cytisus Laburnum. nigricans. Chorozema ilicifolium. Amorpha sp. Phaseolus sp. Prunus sylvestris. Laurocerasus! Rosa sp.! Spiræa sp.! Cotoneaster microphylla! Ailanthus glandulosus. *Fraxinus Ornus! * excelsior! Melia Azedarach. Xanthoxylum sp.! Sambucus nigra.! Aucuba japonica. Erica sp. cult. Jasminum nudiflorum! officinale! Olea europoea. Punica Granatum. Ilex aquifolium! Daphne indica. Daphne odora. Suæda fruticosa. Ulmus campestris. Alnus incana. Salix vitellina, &c.! Thuja orientalis. Pinus pinaster! sylvestris! Abies excelsa! Taxus baccata. Larix europoea.

ENDOGENS.

Lilium Martagon. candidum! *Fritillaria imperialis! Asparagus officinalis! Hyacinthus orientalis! Tamus communis! Narcissi sp.! Gladiolus sp. Zea Mays. Filices.

See also--Moquin-Tandon, 'Elem. Ter. Veget.,' p. 146; C. O. Weber, 'Verhandl. Nat. Hist.,' Vereins, f. d. Preuss., Rheinl. und Westphal., 1860, p. 347, tab. vii; Hallier, 'Phytopathol.,' p. 128; Boehmer, 'De plantis Fasciatis,' Wittenb., 1752.

=Cohesion of foliar organs.=--This takes place in several ways, and in very various degrees; the simplest case is that characterised by the cohesion of the margins of the same organ, as in the condition called perfoliate in descriptive works, and which is due either to a cohesion of the margins of the basal lobes of the leaf, or to the development of the leaf in a sheathing or tubular manner. As an abnormal occurrence, I have met with this perfoliation in a leaf of _Goodenia ovata_. The condition in question is often loosely confounded with connation, or the union of two leaves by their bases. In other cases the union takes place between the margins of two or more leaves.

=Cohesion of margins of single organs.=--The leaves of Hazels may often be found with their margins coherent at the base, so as to become peltate, while in other cases, the disc of the leaf is so depressed that a true pitcher is formed. This happens also in the Lime _Tilia_, in which genus pitcher- or hood-like leaves (_folia cucullata_) may frequently be met with. There are trees with leaves of this character in the cemetery of a Cistercian Monastery at Sedlitz, on which it is said that certain monks were once hung: hence the legend has arisen, that the peculiar form of the leaf was given in order to perpetuate the memory of the martyred monks. ('Bayer. Monogr. _Tiliæ_,' Berlin, 1861.) It is also stated that this condition is not perpetuated by grafting.

I have in my possession a leaf of _Antirrhinum majus_, and also a specimen of _Pelargonium_, wherein the blade of the leaf is funnel-like, and the petiole is cylindrical, not compressed, and grooved on the upper surface, as is usually the case. A comparison of the leaves of _Pelargonium peltatum_ with those of _P. cucullatum_ ('Cav. Diss.,' tab., 106) will show how easy the passage is from a peltate to a tubular leaf. In these cases the tubular form may rather be due to dilatation than to cohesion. M. Kickx[16] mentions an instance of the kind in the leaves of a species of _Nicotiana_, and also figures the leaf of a rose in which two opposite leaflets presented themselves in the form of stalked cups. Schlechtendal[17] notices something of the same kind in the leaf of _Amorpha fruticosa_; Treviranus[18] in that of _Aristolochia Sipho_.

M. Puel[19] describes a leaf of _Polygonatum multiflorum_, the margins of which were so completely united together, as only to leave a circular aperture at the top, through which passed the ends of the leaves. The Rev. Mr. Hincks, at the meeting of the British Association at Newcastle (1838), showed a leaf of a Tulip, whose margins were so united that the whole leaf served as a hood, and was carried upwards by the growing flower like the calyptra of a Moss.

The margins of the stipules are also occasionally united, so as to form a little horn-shaped tube. I have met with instances of this kind in the common white clover, _Trifolium repens_, where on each side of the base of the petiole the stipules had the form just indicated. That the bracts also may assume this condition, may be inferred from the peculiar horn-like structures of _Marcgraavia_, which appear to originate from the union of the margins of the reflected leaf.

=Tubular petals= occur normally in some flowers, as _Helleborus_, _Epimedium_, _Viola_, &c., and as an exceptional occurrence I have seen them in _Ranunculus repens_, while in _Eranthis hyemalis_ transitions may frequently be seen between the flat outer segments of the perianth and the tubular petals. To Dr. Sankey, of Sandywell Park, I am indebted for the flower of a Pelargonium, in which one of the petals had the form of a cup supported on a long stalk. This cup-shaped organ was placed at the back of the flower, and had the dark colour proper to the petals in that situation. I have seen a petal of Clarkia similarly tubular, while some of the cultivated varieties of _Primula sinensis_ exhibit tubular petals so perfect in shape as closely to resemble perfect corollas.

Like the petals, the stamens, and even the styles, assume a hollow tubular form. This change of form in the case of the stamens is, of course, usually attended by the petaloid expansion of the filament, or anther, and the more or less complete obliteration of the pollen sacs, as in Fuchsias, and in some double-flowered Antirrhinums.[20] So also in some semi-double varieties of _Narcissus poeticus_, and in _Aquilegia_. By the late Professor Charles Morren, this affection of the stamens and pistils was called _Solenaidie_,[21] but as a similar condition exists in other organs, it hardly seems worth while to adopt a special term for the phenomenon, as it presents itself in one set of organs.

In many of these cases it is difficult to say whether the cup-like or tubular form is due to a dilatation or hollowing out of the organ affected, or to a fusion of its edges. The arrangement of the veins will in some cases supply the clue, and in others the regularity of form will indicate the nature of the malformation, for in those instances where the cup is the result of expansion, its margin is more likely to be regular and even than in those where the hollow form is the result of fusion.

=Cohesion of several organs by their margins:--leaves, &c.=--The union of the margins of two or more different organs is of more common occurrence than the preceding, the leaves being frequently subjected to this change. Occasionally, the leaflets of a compound leaf have been observed united by their margins, as in the strawberry, the white trefoil, and others. Sometimes the union takes place by means of the stalks only. I have an instance of this in a Pelargonium, in _Tropæolum majus_, and _Strelitzia regina_; in other cases, the whole extent of the leaf becomes joined to its neighbour, the leaves thus becoming completely united by their edges, as in those of _Justicia_, _oxyphylla_.[22] M. Clos[23] has observed the same thing in the leaves of the lentil _Ervum lens_, conjoined with fasciation of the stem, and many other examples might be given. Some of the recorded cases are probably really due to fission of one leaf into two rather than to fusion. Although usually the lower portions of the leaf are united together, leaving the upper parts more or less detached, there are some instances in which the margins of the leaf at their upper portion have been noticed to be coherent, while their lower portions, with their stalks, were completely free.[24]

Cohesion of the leaves frequently accompanies the union of the branches and fasciation as might have been anticipated. Moquin cites the fenestrated leaves of _Dracontium pertusum_, as well as some cases of a similar kind that are occasionally met with, as instances of the cohesion of the margins at the base and apex of the leaf, which thus appears perforated. This appearance, however, is probably due to some other cause. When the leaves are verticillate and numerous, and they become coherent by their margins, they form a foliaceous tube around the stem. When there are but two opposite leaves, and these become united by their margins, we have a state of things precisely resembling that to which the term connate is applied.

Fusion of the edges of the cotyledons also occasionally takes place, as in _Ebenus cretica_.[25] It has also been observed in _Tithonia_, and is of constant occurrence in the seed leaves of some _Mesembryanthema_. This condition must be carefully distinguished from the very similar appearance produced by quite a different cause, viz., the splitting of one cotyledon into two, which gives rise to the appearance as if two were partially united together.

Some of the ascidia or pitcher-like formations are due to the cohesion of the margins of two leaves, as in a specimen of _Crassula arborescens_, observed by C. Morren.

The stipules may also be fused together in different ways; their edges sometimes cohere between the leaf and the stem, and thus form a solitary intra-axillary stipule. At other times they become united in such a manner as to produce a single notched stipule opposite to the leaf. Again, in other cases, they are so united on each side of the stem, that in place of four there seem only to exist two, common to the two leaves as in the Hop.

To the Rev. M. J. Berkeley I am indebted for specimens of a curious pitcher-like formation in the garden Pea. The structure in question consisted of a stalked foliaceous cup proceeding from the inflorescence. On examination of the ordinary inflorescence, there will be seen at the base of the upper of two flowers a small rudimentary bract, having a swollen circular or ring-like base, from which proceeds a small awl-shaped process, representing the midrib of an abortive leaf. In some of Mr. Berkeley's specimens, the stipules were developed as leafy appendages at the base of the leaf-stalk or midrib, the latter retaining its shortened form, while, in others, the two stipules had become connate into a cup, and all trace of the midrib was lost. The cup in question would thus seem to have been formed from the connation of two stipules which are ordinarily abortive.

Cohesion of the bracts by their edges, so as to form a tubular involucre, or by their surfaces, so as to form a cupule, is not of uncommon occurrence, under natural conditions, and may be met with in plants which ordinarily do not exhibit this appearance.

=Cohesion of the sepals= in a normally polypetalous calyx renders the latter gamosepalous, and is not of uncommon occurrence, to a partial extent, though rarely met with complete. I have observed a junction of the sepals to be one of the commonest malformations among Orchids, indeed such a state of things occurs normally in _Masdevallia Cypripedium_, &c. An illustration of this occurrence is given by Mr. J. T. Moggridge in _Ophrys insectifera_, in 'Seemann's Journal of Botany,' 1866, p. 168, tab. 47. In Orchids, this cohesion of sepals is very often co-existent with other more important changes, such as absence of the labellum, dislocation of the parts of the flower, &c.

=Cohesion of the petals.=--Linnæus mentions the occurrence of cohesion of the petals in _Saponaria.[26]_ Moquin notices a Rose in which the petals were united into a long tube, their upper portions were free and bent downwards, forming a sort of irregular limb. An instance of the polypetalous regular perianth of _Clematis viticella_ being changed into a monopetalous irregular one, like the corolla of Labiates, is recorded by Jaeger.[27] There is in cultivation a variety of _Papaver bracteatum_, in which the petals are united by their margins so as to form a large cup. Under normal circumstances, the petals become fused together by their edges along their whole extent, at the base only, at the apex only, as in the Vine, or at the base and apex, leaving the central portions detached. Indications of the junction of the petals may generally be traced by the arrangement of the veins, or by the notches or lobes left by imperfect union. In Crocuses I have frequently met with cohesion of the segments of the perianth, by means of their surfaces, but the union was confined to the centre of the segment, leaving the rest of the surfaces free.

=Cohesion of the stamens.=--Under natural circumstances, cohesion of the stamens is said to take place either by the union of their filaments, so as to form one, two, or more parcels (Monadelphia, Diadelphia, Polyadelphia); at other times, by the cohesion of the anthers (Syngenesia), in which latter case the union is generally very slight. It must be remembered, however, that the so-called cohesion of the filaments is in many cases due rather to the formation of compound stamens, _i.e._ to the formation from one original staminal tubercle of numerous secondary ones, so that the process is rather one of over development than of fusion or of disjunction. These conditions may be met with as accidental occurrences in plants or in flowers, not usually showing this arrangement. Thus, for instance, Professor Andersson, of Stockholm, describes a monstrosity of _Salix calyculata_, in which the stamens were so united together as to form a tube open at the top like a follicle.[28] This is an exaggerated degree of that fusion which exists normally in _Salix monandra_, in Cucurbits and other plants.

=Cohesion of the pistils= is also of very frequent occurrence in plants, under ordinary circumstances, but is less commonly met with than might have been expected as a teratological phenomenon.

Further details relating to cohesion of the various parts of the flower are cited in Moquin-Tandon, 'El. Ter. Veg.,' p. 248; 'Weber. Verhandl. Nat. Hist. Vereins f. d. Preuss. Rheinl. und Westphal.,' 1860, p. 332, tabs. 6 et 7.

=Formation of ascidia or pitchers.=--In the preceding paragraphs, the formation of tubular or horn-like structures, from the union of the margins of one organ, or from the coalescence, or it may be from the want of separation of various organs, has been alluded to, so that it seems only necessary now, by way of summary, to mention the classification of ascidia proposed by Professor Charles Morren[29], who divides the structures in question into two heads, according as they are formed from one or more leaves. The following list is arranged according to the views of the Belgian savant, and comprises a few additional illustrations. Those to which the ! is affixed have been seen by the writer himself; the * indicates the more frequent occurrence of the phenomenon in some than in other plants. Those plants, such as _Nepenthes_, &c., which occur normally and constantly, are not here included. Possibly some of the cases would be more properly classed under dilatation or excavation.

ASCIDIA.

A. _Monophyllous_.

1. Sarracenia-like pitchers, formed by a single leaf, the edges of which are united for the greater portion of their length, but are disunited near the top, so as to leave an oblique aperture.

*Brassica oleracea (several of the cultivated varieties)! *Tilia europæa! Pelargonium inquinans! Staphylea pinnata. Amorpha fruticosa. Pisum sativum! Lathyrus tuberosus. Vicia sp. Gleditschia sp. Ceratonia siliqua. Trifolium repens! Cassia marylandica. Mimosa Lophantha. Rosa centifolia. gallica. Begonia sp. Bellis perennis! Nicotiana sp. Goodenia ovata! Antirrhinum majus! Vinca rosea. Polygonum orientale. Aristolochia sipho? Codiæum variegatum var.! Spinacia oleracea. Corylus avellana! Polygonatum multiflorum. Xanthosoma appendiculatum!

2. Calyptriform or hood-like pitchers, formed by the complete union of the margins, and falling off by a transverse fissure (as in the calyx of Escholtzia).

Tulipa Gesneriana.

B. _Polyphyllous._

1. Diphyllous, formed by the union of two leaves into a single cup, tube, or funnel, &c.

Pisum sativum (stipules)! Crassula arborescens. Polygonatum multiflorum.

2. Triphyllous, formed by the union of three leaves.

Paris quadrifolia var.

Besides the above varieties of ascidia formed from the union of one or more leaves, there are others which seem to be the result of a peculiar excrescence or hypertrophy of the leaf. Such are some of the curious pitcher-like structures met with occasionally in the leaves of cabbages, lettuces, Aristolochia, &c. See Hypertrophy, cup-like deformities, &c.

In addition to other publications previously mentioned, reference may be made to the following treatises on the subject of ascidia:--Bonnet, 'Rech. Us. Feuilles,' p. 216, tab. xxvi, f. 1, _Brassica_; De Candolle, 'Trans. Hort. Soc.,' t. v, pl. 1, _Brassica_; Id., 'Org. Veget.,' I, 316; 'Bull. Soc. Bot. Fr.,' I, p. 62, _Polygonatum_; 'Bull. Acad. Belg.,' 1851, p. 591, _Rosa_; Hoffmann, 'Tijdschrift v. Natuur. Geschied.,' vol. viii, p. 318, tab. 9, _Ceratonia_; C. Mulder, 'Tijdschrift, &c.,' vol. vi, p. 106, tab. 5, 6, _Trifolium_, _Mimosa_, _Staphylea_;' Molkenboer,' p. 115, t. 4, _Brassica_.

FOOTNOTES:

[10] See a curious instance of this kind in the branches of _Pinus_. 'Regel. Garten Flora,' vol. 8, tab. 268.

[11] 'Bull. Soc. Bot. France,' 1860, p. 881.

[12] Ibid., 1861, p. 708.

[13] Ibid., 1860, p. 923.

[14] 'Proc. Linn. Soc.,' April 5, 1853.

[15] 'Organ. Végét.,' pl. iii, fig. 1.

[16] 'Bull. Acad. Roy. Bruxelles,' t. xviii, p. i and p. 591.

[17] 'Linnæa,' tom. 13, p. 383.

[18] 'Verhandl. Nat. Hist. Vereins,' 1859, Bonn, tom. xvi, tab. 3.

[19] 'Bull. Soc. Bot. Fr.,' vol. i, p. 62.

[20] 'Report of Internat. Bot. Congress,' London, 1866, p. 131, tab. vii, figs. 10-13.

[21] 'Bull. Acad. Roy. Belg.,' t. xviii, 2nd part, p. 179.

[22] D. C., 'Organ. Végét.,' pl. xvii, fig. 3, and pl. xlviii, fig. 2.

[23] 'Mém. Acad. Toulouse,' 1862.

[24] Bonnet, 'Recherches Us. feuill.,' pl. xxi, fig. 2.

[25] De Candolle, 'Mém. Lég.,' pl. v, fig. 14.

[26] 'Phil. Bot.,' § 125.

[27] 'Nov. Act. Acad. Nat. Cur.,' 14, p. 642, t. xxxvii.

[28] 'Journal of the Linn. Soc. Bot.,' vol. iv, p. 55.

[29] 'Bull. Acad. Roy. Bruxelles,' 1838, t. v, p. 582. 'Bull. Acad. Roy. Belg.,' 1852, t. xix, part iii, p. 437.