Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/144

Rh BOTANY [REPRODUCTIVE ORGANS. This corolla occurs in many Composite plants, as in the Plate IX. florets of Dandelion, Daisy, and Chicory. The number of divisions at the apex indicates the number of united petals, some of which, however, may be abortive. Occasionally some of the petals become more united than others, and then the corolla assumes a bilabiate, or two-lipped form, as seen in the division of Composites called Labiatiflone. In Grasses and Sedges, in place of verticillate leaves forming the flower, there are alternate scales or glumes. The flowers of Grasses usually occur in spikelets (fig. 212), which consist of one or two glumes a, covering several flowers b. The spikelets are associated in spikes or panicles. In Wheat these spikelets are arranged alternately along a common rachis. Each spikelet consists of two empty glumes a, a, having the form represented in fig. 212, and enclosing flowers composed of scales (pake? Fi ? . 212. Fig. 213. Fig. 214. FIG. 212. A spikelet of Whcnt (Triticum), consisting of two glumes a, a, enclosing several flowers 6, 6, which ni-e composed of two pales (palese; covering the essential organs of reproduction. The stamens s hang out by long, slender, thread-like filaments. The individual glumes and palesc are placed alternately on the floral axis. FIG. 213. Flower of Oat (Arena saliva), with the two glumes, and the outer glumella or palea removed. The inner glumella, flowering glume, or palea pi, is seen, of a lanceolate form, and bidentate at the apex. By removing the outer glumella there are seen two scales (lodiculce, squama?) sq, with the three stamens and two feathery styles. FIG. 214. Pistillifcrous or pistillate flower of a Sedge (Carex) with a single glume or scale s. The pistil is covered by an urceolatc glumaccous bag u, called perigynium. There is one style st, with three stigmas at its summit. or glumellce), which are placed at different heights in an alternate manner. In the flower of the Oat (fig. 213), after removing the outer pale or glumella?, the inner one pi is seen with two scales (lodiculce or squama?) sq, at the base, enclosing the essential organs of reproduction. The palete of grasses are called by some flowering glumes, while hypogynous scales (lodicula)) within them are con sidered as the rudimentary perianth. In Wheat (Triticum) there are two empty glumes and two flowering glumes, or, as some say, one flowering glume and one pale. In the Oat (Avena) there are two empty glumes, usually three flowering glumes with awns, and two lodicules representing the perianth. In Sedges (Carices) the male flowers are borne on scales, and so are the female, as shown in fig. 214, in which the scale s is placed on one side. Within the scale the female flower is situated, having a peculiar bag- like covering u, termed perigynium. The parts of the corolla frequently adhere to those of the calyx, and any change in the latter causes also an alteration in the former. Petals are sometimes suppressed, and sometimes the whole corolla is absent. In Amorpha and Afzelia the corolla is reduced to a single petal, and in some other Leguminous plants it is entirely wanting. In the natural order Ranunculaces?, some genera, such as Ranunculus, Globe-flower, and Pyccmy, have both calyx and corolla, while others, such as Clematis, Anemone, and Caltha, have only a coloured calyx. Flowers become double by the multiplication of the parts of the coralline whorl. This arises in general from a metamorphosis of the stamens. Union of separate flowers (synanthos) occasion ally occurs, and the adhesion which thus takes place causes various changes ic. the whorls. Flowers may be united by their peduncles, as seen in some anomalous specimens of Dandelion, Hyacinth, and Centaury ; or by their outer parts, such as the calyx. At other times there is a complete fusion, as it were, of all the parts of the flowers, some continuing normal, others being suppressed or abortive. Certain abnormal appearances occur in the petals of some Nectaries. flowers, which received in former days the name of nectaries. The term nectary was very vaguely applied by Linnaeus to any part of the flower which presented an unusual aspect, as the crown (corona) of Narcissus, the fringes of the Passion-flower, &c. If the name is retained rt ought pro perly to include only those parts which secrete a honey-like matter, as the glandular depression at the base of the perianth of the Fritillary, or on the petal of Ranunculus, or on the stamens of Rutacese. The honey secreted by flowers attracts insects, which, by conveying the pollen to the stigma, effect fertilization. What have usually, how ever, been called nectaries, are mere modifications of some part of the flower, especially of the corolla and stamens, produced either by degeneration or outgrowth, or by dila- mination, chorisis, or deduplication. Of this nature are the scales on the petals in Lychnis, Silenc, Cynogiossum, and Ranunculus (fig. 202). Others consider these outgrowths of the petal to be formed in the same way as the ligules of Grasses. Corollas having these scaly appendages are some times denominated appendiculate. In Cuscuta and Samolus Plate X. the scales are alternate with the petals, and may represent altered stamens. The parts formerly called nectaries are mere modifications of the corolla or stamens. Thus the so- called horn-like nectaries under the galeate sepal of Aconite (fig. 205-) are modified petals, so also are the tubular nectaries of Hellebore (fig. 203). The nectaries of Menyanthes and of Iris consist of hairs developed on the petals. Those oi Parnassia and the Passion-flower, Stapelia, Asclepias, and Canna, are fringes, rays, and processes, which are probably modifications of stamens ; and some consider the crown of Narcissus as consisting of a membrane similar to that which unites the stamens in Pancratium. It is sometimes difficult to say whether these nectaries are to be referred to the corolline or to the staminal row. The paraphyses of the Passion-flower, the crown of Narcissus, and the coronet of Stapelia are referred sometimes to the one and sometimes to the other. In general, they may be said to belong to that series with which they are immediately connected. Some have given names indicating the parts of which they are modifications, by prefixing the term para, using such terms as paracorolla and parastemoncs. Petals are attached to the axis usually by a narrow base, but occasionally the base is larger than the limb, as in the Orange flower. When this attachment takes place by an articulation, the petals fall off either immediately after expansion (caducous), or after fertilization (deciduous). A corolla which is continuous with the axis and not articu lated to it, as in Campanula and Heaths, may be persistent, and remain in a withered or marccscent state while the fruit is ripening. A gamopetalous corolla falls off in one piece ; but sometimes the base of the corolla remains per sistent, as in Rhinanthus and Orobanche. II. ESSENTIAL ORGANS. These organs are the stamens and ticpistil, the lattei Essential containing the seeds or germs of young plants, and corre- r s ans of spending to the female, while the former produces a powder necessary for fecundation, and is looked upon as performing the part of the male. The presence of both is required in