[166] 'Phytanth.,' n. 36, _d._

[167] 'Ann. Scienc. Nat.,' 3rd series. 1853. vol. xix, p. 251, tab. 14.

[168] Carriere, 'Revue Horticole.' 1868, p. 184.

[169] 'Gard. Chron.,' 1858, p. 556.

[170] 1863, p. 556, &c.

[171] 'Ann. Nat. Hist.,' 1845, vol. xvi, p. 355.

[172] See also Lindley, 'Veg. Kingd.,' p. 109 et 116_a_, where the views of Raspail, R. Brown, Mohl, Henslow, and others, are discussed.

[173] It has been observed that if a plant is supplied with copious nourishment the flowering-period is delayed; but that moderate or even scanty nourishment accelerates it. Goethe, 'Metam.,' -- 30. See also Wolff, 'Theoria Generationis,' 1759; Linn. 'Prolepsis,' ---- 3 and 10.

[174] Moquin-Tandon, p. 384; also Lindl., 'Elements of Botany,' p. 65, fig. 130; "Theory of Horticulture," p. 86. 'Gard. Chron.,' 1851, p. 723; Irmish, 'Flora,' 1858, p. 38, &c.

[175] Caspary, 'Bull. Soc. Bot. Fr.,' vol. vi, 1859, p. 235; also Payer, ibid., vol. i, 1854. p. 283.

[176] Trecul, 'Ann. Sc. Nat.,' 2nd ser., vol. xx, p. 339.

[177] 'Bull. Soc. Bot. Fr.,' vol. vii, 1858, p. 331.

[178] 'Bull. Soc. Bot. Fr.,' vol. i. p. 306, vol. v, p. 115. 'Ill.u.s.tr.

Hortic.,' xii, 1865, Misc. 79. 'Rev. Horticole,' 1860 p. 204, et 1867 p.

43.

[179] 'Bull. Soc. Bot. Fr.,' 1858, p. 685.

[180] The structure of this flower is discussed at some length in a paper by the author on axillary prolification. 'Trans. Linn. Soc.,' vol.

xxiii, p. 486, t. liv. fig. 3. See also 'Clos. Bull. Soc. Bot. Fr.,'

vol. v, 1855, p. 672. Seringe et Heyland, 'Bull. Bot.,' i, p. 8. 'Pallas Enum. Plant. Hort. Demidoff,' append, c, ic.

[181] 'Adansonia,' i, 181.

[182] 'Adansonia.' vol. iii, p. 351, tab. xii.

[183] 'Elem. Terat. Veget.,' p, 218.

[184] Masters, 'Journ. Linn. Soc.,' vol. ix, 1866, p. 334.

[185] 'Trans. Linn. Soc.,' vol. xxiv, p. 143. tab. xxiv.

[186] 'Brit. a.s.soc. Report,' Dundee, 1867; and Seemann's 'Journal of Botany,' 1867, p. 319, tab. lxxii, figs. B 1-9.

[187] Duval Jouve, 'Hist. Equiset. France.' 1864, p. 154.

[188] 'Flora,' t. xxiv, 1841, p. 340.

[189] Moore, 'Nature-Printed British Ferns,' 8vo edition, vol. ii. p.

135. tab. lx.x.xv, B, &c.

CHAPTER IV.

HETEROGAMY.

This term is here intended to apply to all those cases in which the arrangement of the s.e.xual organs is different from what it is habitually. It is evident that in many instances there is no malformation, no monstrosity, but rather a restoration of organs habitually suppressed, a tendency towards structural completeness rather than the reverse. It must be also understood that the following remarks apply to structural points only, and are not intended to include the question of function. The occurrence of heteromorphic unions renders it necessary to keep in mind that plants hermaphrodite as to structure are by no means necessarily so as to function.

The simplest case of this alteration in the relative position of the s.e.xes is that which occurs in monoecious plants, where the male and female flowers have a definite position, but which in exceptional instances is altered.

=Change in the relative position of male and female flowers= may thus occur in any monoecious plant. Cultivated maize, _Zea Mays_, frequently exhibits alterations of this kind; under ordinary circ.u.mstances, the male inflorescence is a compound spike, occupying the extremity of the stem, while the female flowers are borne in simple spikes at a lower level, but specimens may now and then be found where the s.e.xes are mixed in the same inflorescence; the upper branching panicle usually containing male flowers only, under these circ.u.mstances, bears female flowers also.[190] In like manner, but less frequently, the female inflorescence occasionally produces male flowers as well.

Among the species of _Carex_ it is a common thing for the terminal spike to consist of male flowers at the top, and female flowers at the base; the converse of this, where the female flowers are at the summit of the spike, is much more uncommon. An ill.u.s.tration of this occurrence is given in the figure (fig. 100). Among the _Coniferae_ numerous instances have been recorded of the presence of male and female flowers on the same spike, thus Mr. now Professor Alexander d.i.c.kson exhibited at the Botanical Society of Edinburgh in July, 1860, some malformed cones of _Abies excelsa_, in which the inferior part of the axis was covered with stamens, whilst the terminal portion produced bracts and scales like an ordinary female cone. The stamens of the lower division were serially continuous with the bracts above. Some of the lower scales of the female portion were in the axils of the uppermost stamens, which last were somewhat modified, the anther cells being diminished, whilst the scale-like crest had become more elongated and pointed, in fact, more or less resembling the ordinary bracts.[191] Mohl, Schleiden, and A. Braun have observed similar cones in _Pinus alba_, and Cramer figures and describes androgynous cones in _Larix microcarpa_. C. A. Meyer ('Bull.

Phys. Math.,' t. x, 1850) also describes some catkins of _Alnus fruticosa_ which bore male flowers at the top, and female flowers at the base.

[Ill.u.s.tration: FIG. 100.--Spike of _Carex acuta_, with female flowers at the summit.]

On the subject of this section the reader may consult A.

Braun,. 'Das Individ.,' 1853, p. 65. Caspary, 'De Abietin.

flor. fem. struct. morphol.' Schleiden. 'Principles,' English edition, p. 299. Mohl, 'Verm. Schrift.,' p. 45. Meyen in 'Wiegm. Archiv.,' 1838, p. 155. Cramer, 'Bildungsabweich,' p.

4, tab. v, figs. 13-17. Parlatore, 'Ann. Sc. Nat.,' ser. iv, vol. xvi, p. 215, tab. 13A. See also under the head of Prolification, Subst.i.tutions, &c.

=Change from the monoecious to the dioecious condition.=--This is of less frequent occurrence than might have been antic.i.p.ated. In the 'Gardeners' Chronicle,' 1847, pp. 541 and 558, several instances are noted of walnut trees bearing female flowers to the exclusion of males.

The mulberry tree has also been noticed to produce female blossoms only, while in other plants male flowers only are developed.

It seems probable that the age of the plant may have something to do with this production of flowers of one s.e.x to the exclusion of the other.

=Change from the dioecious to the monoecious condition.--Androgynism.=-- This is of far more common occurrence than the preceding.

[Ill.u.s.tration: FIG. 101.--Monoecious inflorescence of Hop.]

In the hop (_Humulus Lupulus_), when monoecious, the female catkins are usually borne on the ends of the branches as shown in the cut (fig.

101), and a similar thing has been noticed in _Urtica dioica_ by Clos, 'Bull. Soc. Bot. France,' vol. 9, p. 7.

Baillon ('Etudes du groupe des Euphorbiacees,' p. 205) mentions the following species of that order as having been seen by him with monoecious inflorescence: _Schismatopera distichophylla_, _Mozinna peltata_, _Hermesia castaneifolia_. Oliver mentions ('Hook. Icon.

Plant.,' t. 1044) that in _Leitneria floridana_ the upper scales of the male catkin occasionally subtend an ovary.

It would seem that external conditions have some effect in determining the formation of one s.e.x, as in some species of _Carex_, while in the case of _Salix repens_, Hampe[192] says that when grown partially or for a time under water, those twigs which are thrust up above the surface bear female flowers, while those twigs that blossom after the water is dried up, produce male flowers only.

Carriere[193] says that a plant of _Stauntonia latifolia_ which for some years produced stamens only, now produces flowers of both s.e.xes; it was dioecious, but is now monoecious. The same author alludes to a similar occurrence in _Juniperus Virginiana_. The hops is also said to vary in s.e.xual characteristics from time to time.[194] In addition to the genera, already named, in which this production of flowers of both s.e.xes has been observed may be mentioned _Taxus! Gunnera! Urtica!

Mercurialis! Restio! Cannabis! Salix! Humulus!_ as well as others in which the change is less frequent.

Among cryptogams a similar change occurs. As an ill.u.s.tration may be cited _Leucobryum giganteum_, as quoted from Muller in Henfrey's 'Botanical Gazette,' i, p. 100.