[Ill.u.s.tration: FIG. 182.--Broccoli, with six perfect heads on one stalk ('Gard. Chron.,' 1856, Oct. 25).]

=Increased number of florets= in the individual spikelets of gra.s.ses is also met with under some circ.u.mstances. I have seen this in _Hordeum_ and _Lolium_, and an instance is figured in _Avena_ by Dr.

Wiegmann.[389] M. Duval Jouve[390] records a similar occurrence in _Catabrosa aquatica_, the spikelets of which contained from two to seven flowers.[391]

FOOTNOTES:

[379] 'Phil Bot.,' -- 274.

[380] 'El. Ter. Veget.,' p. 392.

[381] 'Bull. Acad. Belg.,' xvii, part ii, p. 38.

[382] 'Bull. Soc. Bot. Fr.,' vol. iv, 1857. p. 760.

[383] Ibid., vol. viii, 1861, p. 159.

[384] See 'Gard. Chron.,' July, 1866, p. 656, and Clusius, 'Plant.

Rar.,' lib. 2, p. 143, _Tulipa serotina_ [Greek: polyklades], _minor_, _&c._ Hort. Eysttett. Plant. Vern.,' fol. 12.

[385] 'Jaeger de Pini sylvestris monstrositate,' Stuttgardt, 1828.

[386] Cited in 'Bull. Soc. Bot. Fr.,' xiv, p. 265.

[387] Duval Jouve, 'Hist. Nat. Equiset. Fr.,' tab. 8, also Milde, 'Nov.

Act. Acad. Nat. Cur.,' t. xxvi, part 2. For branched inflorescence of orchids, see 'Reichenbach Proc. Lond. Bot. Congress,' 1866, p. 121.

[388] 'Bull. Soc. Bot. Fr.,' vi, 266, vii, 457. Irmisch, 'Knollen und Zwiebelgew.,' tab. 7, figs. 10, 11.

[389] 'Flora,' 1831, p. 5, tab. i; see also Hanstein, 'Flora,' 1857, p.

513. Schlechtendal, 'Bot. Zeit.,' xviii, p. 381.

[390] 'Bull. Soc. Bot. Fr.,' ix, p. 8.

[391] It will be seen, from what has been just said, that in some of the cases where the axile organs, branches, &c., appear to be multiplied, the increased number is due to subdivision rather than to renewed formation (see Fission). Of this last description is an instance which came under the writer's notice after the section relating to that subject was in print, and which may therefore here be alluded to. The instance is that of the subdivision of the leaf-like organs of _Sciadopitys verticillata_. In one instance the pseudo leaf divided, and from the division proceeded a little axis, bearing at its summit a verticil of pseudo leaves. This division and formation of new axes and verticils affords ample confirmation of the opinion thrown out by Professor Alexander d.i.c.kson, that the apparent leaves of this plant were really branches: see 'Revue Horticole,' 1867, and 'Report. Bot.

Congress,' London, 1866, p. 124.

CHAPTER II.

MULTIPLICATION OF FOLIAR ORGANS.

The cases referrible to this head may be ranged under two sections according as the increase is due to plurality of ordinarily single organs, or to an increase in the number of verticils or whorls.

When, in place of a single leaf organ two or more are really or in appearance present the occurrence may be due to one of several causes; among them may be mentioned an actual formation of parts in unwonted number, hypertrophy or enation, chorisis or fission, disjunction, adhesion of one leaf to another or to the stem, as in some of the leaves called "geminate," wherein the two leaves, though apparently in juxtaposition, yet originate from different parts of the stem, but by coalescence or lack of separation produce the impression as if they sprang from the same node. In the adult state it is not always possible to ascertain with certainty to which of these causes the increase in the number of leaves is due, though a clue to the real state of things may be gained from attention to the distribution of the veins, to the arrangement or phyllotaxy of the leaves, the size and position of the supernumerary organs, &c.

The term "phyllomania," as ordinarily used, is applied to an unwonted development of leafy tissue, as in some begonias where the scales or ramenta are replaced by small leaflets, or as in some cabbage leaves, from the surface of which project, at right angles to the primary plane, other secondary leafy plates; but these are, strictly speaking, cases of hypertrophy (see Hypertrophy).

Those instances in which the actual number of leaves is increased, so that in place of one there are more leaflets, may be included under the term "pleiophylly," which may serve to designate both the appearance of two or more leaves in the place usually occupied by a single one, and also those normally compound leaves in which the number of leaflets is greater than usual.

The increased number of leaves in a whorl may well be designated as "polyphylly," using the word in the same sense as in ordinary descriptive botany, while "pleiotaxy" may be applied to those cases in which the number of whorls is increased.

[Ill.u.s.tration: FIG. 183.--Supernumerary leaflet, _Ulmus campestris_.]

=Pleiophylly.=--As above stated, this term is proposed to designate those cases in which there is an absolute increase in the number of leaves starting from one particular point, as well as those in which the number of leaflets in a compound leaf is preternaturally increased. The simplest cases are such as are figured in the adjacent cuts, wherein, in place of a single leaf, two are produced in the elm. In the one case the new leaflet springs from the apex of the petiole and partially fills the s.p.a.ce consequent on the obliquity of the base of the leaf. In the other it would seem as if two distinct leaves emerged from the stem in juxtaposition. This is probably due to a lateral chorisis or subdivision of the primitive tubercle or growing point, followed by a like subdivision of the vascular bundle supplying it. There are certain varieties of elm that very generally present this anomaly on their rank, coa.r.s.e, growing shoots. In these cases the new growths have the same direction as the primary one, but in other cases the supplementary production is exactly reversed in direction. Thus, in the common hazel (_Corylus_) a second smaller leaf proceeding from the end of the leaf-stalk at the base of the primary one may frequently be seen. M.

Germain de Saint Pierre records an instance in a mulberry leaf, from the base of which proceeded a large leafy expansion divided into two tubular, horn-like projections, and in the centre a thread-like process representing the midrib and terminated by a small two-lipped limb.[392]

Dr. Ferdinand Muller speaks of a leaf of _Pomaderris elliptica_ as bearing a secondary leaf on its under surface.[393]

[Ill.u.s.tration: FIG. 184.--Supernumerary leaf, _Ulmus montana_.]

[Ill.u.s.tration: FIG. 185.--Supernumerary leaf of hazel.]

The leaves of _Heterocentron macrodon_ have likewise been observed occasionally to produce leaflets from their upper surface.

To this production of leaves from leaves the late Professor Morren applied the term "autophyllogeny."[394] The Belgian botanist figures a small perfect leaf springing from the nerves of the upper surface of the primary leaf in a species of _Miconia_. As in the hazel, the direction of the advent.i.tious leaf is inversely that of the primary one, the upper surface of the supernumerary leaflet being turned towards the corresponding surface of the normal leaf. A similar occurrence took place in _Gesnera zebrina_, but the new growth in this case sprang from the lower face of the leaf. Morren explains the appearances in question by supposing that the supplementary leaf is one of a pair belonging to a bud borne on a slender stalk. This stalk and one of the bud-leaves are supposed to be inseparably united with the primary leaf. But there is no reason at all for supposing the existence of adhesion in these cases; no trace of any such union is to be seen. A much more natural explanation is that, from some cause or another, development at the apex of the petiole or on the surface of the nerves, instead of taking place in one plane only, as usual, takes place in more than one, thus showing the close relationship, if not the intrinsic ident.i.ty, between the leaf-stalk and its continuation, the midrib, with the branch and its subdivisions. The form of the leaf-stalk and the arrangement of the vascular bundles in a circle in the case of the hazel, before alluded to, bear out this notion. Such cases are significant in reference to the notion propounded by M. Casimir de Candolle, that the leaf is the equivalent of a branch in which the upper portion of the vascular circle is abortive.[395]

Compound leaves, as has been stated, occasionally produce an extra number of leaflets; one of the most familiar ill.u.s.trations of this is in the case of the four-leaved shamrock (_Trifolium repens_), which was gathered at night-time during the full moon by sorceresses, who mixed it with vervain and other ingredients, while young girls in search of a token of perfect happiness made quest of the plant by day. Linne, who in this matter, at any rate, had less than his usual feeling for romance, says of the four-leaved trefoil that it differs no more from the ordinary trefoil than a man with six fingers differs from one provided with the ordinary number. It should be stated that five and six advent.i.tious leaflets are found almost as frequently as four.

Walpers describes a case where the leaf of _T. repens_ bore seven leaflets. Schlechtendal alludes to a similar increase in number in _Cytisus Laburnum_, and many other instances might be cited.

For figures or descriptions of four-leaved shamrocks the reader is referred to Lobel, 'Stirp. Advers.,' Nov., p. 382.

Tabernaemonta.n.u.s 'Krauterbuch,' S. 222. Schlechtendal, 'Bot.

Zeit.,' ix, p. 583, xiv, p. 71. Maugin, 'Bull. Soc Bot. Fr.,'

1866, t. xiii, p. 279. See also Cramer, 'Bildungsabweich,' p.

92. Walpers, 'Linnaea,' 1840, p. 362 (7-leaved). Schlechtendal, 'Bot. Zeit.,' 1844, p. 457, _Cytisus_. Wigand, 'Flora,' 1856, p. 706.

Frondiferous leaves have much the appearance of branches provided with leaves, and they may be compared with those instances in which an advent.i.tious bud is placed on the surface or edges of the leaves, as in _Gesnera_, _Cardamine_, &c. In truth, the two conditions merge one into the other, as in some begonias, where the ramenta often become leaf-like and bear small bulbils in the axil.

When frondiferous leaves die the appendages die also, but when a true bud has been formed on a leaf it does not of necessity die with the leaf that bears it, but separates from it and continues to grow independently.

=Increased number of stipules, spathes, &c.=--Seringe relates the occasional presence of two or three additional stipules upon the leaf-stalks of _Salix fragilis_, and even makes a variety (_Salix pendula_, var. _multistipulata_).

An increase in the number of the spathes has been often noticed in Arads[396]. Prof. Alex. Braun has studied this subject in some detail[397]. In _Calla pal.u.s.tris_ the shoot which continues the growth of the plant proceeds from the axil of the last leaf but one; the very last leaf producing no bud, but if accidentally a shoot is developed in this latter situation it produces flowers at once. No leaves are formed, but, on the contrary, two or three spathes surround the spadix, so that the presence of an increased number of spathes in this plant is a.s.sociated with the development of a side shoot from the axil of the last leaf, the situation whence, under natural circ.u.mstances, no shoot at all issues. The supernumerary spathes are not always on the same level, but may be separated by a considerable interval. They vary very much in size, and sometimes a.s.sume the form and appearance of leaves.

Similar anomalies occur in other Arads as _Arum maculatum_, _Richardia aethiopica_, and _Anthurium Scherzerianum_, frequently combined with a leaf-like appearance of the spathes and sometimes with a subdivision of the spadix into two or three branches.

Engelmann relates the occurrence of an increased number of glumes in _Bromus velutinus_ a.s.sociated with suppression of the flowers.

=Polyphylly.=--As previously explained, this term is here applied to those cases in which the members of any particular whorl are increased in number, the whorls themselves not necessarily being augmented.

The simplest cases of this kind are those in which we meet with an unusual number of leaves in a whorl.

=Increased number of leaves in a whorl.=--This may arise from actual multiplication, or from lateral chorisis, or fission. The true nature of the case may usually be ascertained by an examination of the distribution of the veins of the leaves, or of the fibrous cords of the stem, by the relative position of the supernumerary organs, &c.

Among plants with normally opposite leaves the following occasionally produce them in whorls of three:--_Lonicera brachypoda_, _L. Xylosteum_, _Weigela rosea_, _Cornus mas_, _Vinca minor_, &c.

_Paris quadrifolia_ may frequently be met with five leaves in its whorl, or even six.[398]