CHAPTER II.

DIALYSIS.

This term is here made use of in the same sense as in descriptive botany, to indicate the isolation of parts of the same whorl; it is thus the opposite of cohesion. Morren, as has been previously stated, employed the word in a different sense, while Moquin-Tandon[75] included cases of this description under the category of "Disjonctions qui isolent les organes."

Dialysis, as here understood, may be the result of an arrest of development, in consequence of which parts that under ordinary circ.u.mstances would become fused, do not do so; or, on the other hand, it may be the result of an actual separation between parts primitively undivided. As it is not possible in every case to distinguish between the effects of these two diverse causes, no attempt is here made to do so.

=Dialysis of the margins of individual foliar organs.=--In cases where the leaf or leaf-like organ is ordinarily tubular or horn-like in form, owing to the cohesion of its edges, it may happen either from lack of union or from actual separation of the previously united edges, that the tubular shape is replaced by the ordinary flattened expansion. Thus, in _Eranthis hyemalis_, wherein the petals (nectaries) are tubular and the sepals flat, I have met with numerous instances of transition from the one form to the other, as shown in fig. 9, p. 24.

It is, however, in the carpels that this separation occurs most frequently. When these organs appear under the guise of leaves, as they often do, their margins are disunited, so that the carpel becomes flat or open. This happens in the strawberry (_Fragaria_), the columbine (_Aquilegia_), in _Trifolium repens_, _Ranunculus Ficaria_, &c.[76]

=Dialysis of the parts of the same whorl:--calyx.=--The separation of an ordinarily coherent series into its const.i.tuent parts is necessarily of more common occurrence than the foregoing. As here understood, it is the precise converse of cohesion, and it may be represented diagrammatically by a dotted line above the letters denoting the sepals, petals, &c. When this change happens in the calyx we have the gamosepalous condition replaced by the polysepalous one, as thus represented:

S S S S S instead of _____________ S S S S S

as in a calyx of five coherent sepals.

Detachment of this kind occurs not unfrequently, as in _Primula vulgaris_, _Trifolium repens_, &c. In _Rosaceae_ and _Pomaceae_ this separation of the calyx is of the more moment, as it has reference to the structure of the inferior ovary, as will be more fully mentioned hereafter. Here, however, a case recorded by M. J. E. Planchon may be alluded to[77] wherein a quince fruit (_Cydonia_) was surmounted by five leaves, the surface of the pome being marked by as many prominences, which apparently corresponded to the five stalks of the calycine leaves.

In this specimen, then, the inferior position of the ovary appeared to be not so much due to an expansion of the fruit stalk, as to the fusion of the hypertrophied stalks of the sepals. Some of the malformations among Cucurbits point to a similar structure. It is probable that in many of these cases the so-called inferior ovary is partly axial partly foliar, _i.e._, sepaline, and partly carpellary in its nature.

Dialysis of the sepals in calyces that are usually gamosepalous has been most frequently observed in _Rosaceae_, _Pomaceae_, _Umbelliferae_, less commonly in _Leguminosae_, also in the following genera:--_Primula_, _Symphytum_, _Gentiana_, _Campanula_, &c.

[Ill.u.s.tration: FIG. 30.--Dialysis of the sepals and petals in _Correa_.]

=Dialysis of the corolla= is likewise of frequent occurrence, either partially or to such an extent as to render the corolla truly polypetalous. Among _l.a.b.i.atae_ the upper lip of the corolla may be often met with partially cleft, as it is constantly in _Phlomis biloba_, or more markedly among the _Lobeliaceae_.

In the _Compositae_, a similar separation of the petals is not infrequent, thus showing frequent transitional stages between the l.a.b.i.atifloral and tubulifloral divisions respectively. The ligulate corollas also may often be found in Chrysanthemums, Dahlias, &c., more or less deeply divided into their component parts.

A more complete separation occurs not unfrequently in _Campanula_, _Rhododendron_, _Phlox_, _&c._ Figs. 30 and 31 ill.u.s.trate dialysis of the corolla; the first in _Correa_, the second in _Campanula_.

[Ill.u.s.tration: FIG. 31.--Dialysis of the corolla in _Campanula sp._, after De Candolle.]

In the last-named genus, _C. rotundifolia_ has been found with polypetalous flowers in a wild state in the mountains of Canton Neufchatel, Switzerland, and gave rise to the creation of a new genus.

This form is now introduced into gardens.

It must be remembered that in some genera, where this separation of the petals has been met with, there are species in which a similar isolation occurs normally, as in _Rhododendron_. _R. linearilob.u.m_, a j.a.panese species, offers a good ill.u.s.tration of this.

The following list contains the names of the genera in which this separation of the petals of an ordinarily gamopetalous flower takes place most frequently.

Correa.

Campanula! sp. pl.

Polemonium.

Phlox!

Coboea!

Rhododendron!

Erica!

Rhodora.

Azalea!

Compositae! sp. pl.

Lonicera!

Convolvulus!

Pharbitis.

Antirrhinum!

Verbasc.u.m!

Mimulus.

Digitalis!

Orobanche.

Solanum.

Nicotiana.

Gentiana!

Anagallis.

Primula!

Lamium!

Convallaria!

Lilium!

Colchic.u.m!

&c. &c.

This list does not include those very numerous cases in which this change is a.s.sociated with more or less complete frondescence or leafy condition of the petals.

=Dialysis of the stamens.=--A similar isolation of the stamens occurs occasionally; for instance, when Mallows (_Malvaceae_) become double, one of the first stages of the process is often the disjunction of the stamens, and a similar dissociation occurs in _Leguminosae_ and _Compositae_, as in _Tragopogon_, as related by Kirschleger, in _Hypochaeris_ by Wigand, and in _Coreopsis_ by Schlechtendal.

=Dialysis of the carpels.=--In the case of the carpels this disunion is more frequent than in the stamens. M. Seringe[78] figures carpels of _Diplotaxis tenuifolia_ more or less completely separated one from the other; indeed, this separation is very common amongst _Cruciferae_ and _Umbelliferae_.

Generally speaking, the disunion is complicated with frondescence--but not always so. I have, in my herbarium, specimens of _Convallaria majalis_, _Commelyna sp._, and of _Lilium auratum_, in all of which the three carpels are completely disjoined, and present three styles, three stigmas, &c., without any other change. Engelmann[79] speaks of three cla.s.ses of this malformation. 1st, that in which the carpels separate one from the other without opening, as in the lily just alluded to; 2nd, that in which the ovary remains closed, but loses its internal part.i.tions, as in a case mentioned by Moquin in _Stachys sylvatica_, in which, owing to imperfect disjunction, the two bi-lobed carpels were changed into a nearly one-celled capsule;[80] and 3rd, those cases in which the carpels are open and foliaceous.

[Ill.u.s.tration: FIG. 32.--Anomalous form of orange.]

Disjunction is more frequent in dry fruits than in fleshy ones. In the latter instance it happens at an early stage of existence, and the pericarp becomes more or less leafy, losing its faculty of becoming fleshy, as in _Prunus Cerasus_ and _Amygdalus persica_; nevertheless, fleshy fruits sometimes become disunited. I have seen a case similar to that mentioned by M. Alphonse de Candolle in _Solanum esculentum_, in which the pericarp became ruptured, and the placentas protruded. A like occurrence has also been observed in a species of _Melastoma_.[81] This is a.n.a.logous to what happens in _Caulophyllum_ and _Slateria_.

Disjunction of the carpels is not rare in oranges. Sometimes this takes place regularly, at other times irregularly; occasionally in such a manner as to give the appearance of a hand and fingers to the fruit. Of one of these, Ferrari,[82] in the curious volume below cited, speaks thus: "Arbor profusissima, quia dat utraque manu; imo quia vere ma.n.u.s dat in poma conversis; utque magis munifica sit poma ipsa convert.i.t in ma.n.u.s."

M. Duchartre[83] mentions a semi-double flower of orange with eight to ten distinct carpels in a whorl, and occasionally several whorls one above another. De Candolle[84] considers the rind of the orange as a production from the receptacle, and this view is confirmed by the specimens of Duchartre, in which the carpels were quite naked or had a common envelope truncated, and open above to allow of the pa.s.sage of the styles and stigmas.

[Ill.u.s.tration: FIG. 33.--Orange. Showing disjunction of carpels, after Maout.]

[Ill.u.s.tration: FIG. 34.--Section of orange shown in fig. 33 after Maout.]

It frequently happens in conjunction with this separation of the carpels one from the other, that a lack of union manifests itself between the margins of the individual carpels themselves. Very numerous cases of this kind have been recorded, and the double tulips of gardens may be referred to as showing this condition very frequently. In connection with this detachment of the carpels, a change in the mode of placentation is often to be observed, or two or more kinds may be seen in the same pistil, as in double-flowered saponarias, many Crucifers, &c., as alluded to under the head of displacements of the placenta.

FOOTNOTES:

[75] _Loc. cit._, p. 298.

[76] Masters in Seemann's 'Journal of Botany,' 1867, p. 158.

[77] Bull. Soc. Bot. France,' t. xiii, 1866, p. 234.