Bract Sentence Examples
Except where it is terminal it arises, like the leaf-shoot, in the axil of a leaf, which is then known as a bract.
In the male flower the receptacle is "concrescent" or inseparate from the bract in whose axil it originates.
Thus a bract may be regarded, with Haeckel, as a modified umbrella of a medusa, a siphon as its manubrium, and a tentacle as representing a medusan tentacle shifted in attachment from the margin to the sub-umbrella; or a siphon may be compared with a polyp, of which the single tentacle has become shifted so as to be attached to the coenosarc and so on.
Their cones are composed of thin, rounded, closely imbricated scales, each with a more or less conspicuous bract springing from the base.
The female flower consists of a cup-like receptacle, inseparate from the ovary, and bearing at its upper part a bract and two bracteoles.Advertisement
The small flowers are densely crowded on thick fleshy spikes, which are associated with, and often more or less enveloped by, a large leaf (bract), the so-called spathe, which, as in cuckoo-pint, where it is green in colour, Richardia, where it is white, creamy or yellow, Anthurium, where it is a brilliant scarlet, is often the most striking feature of the plant.
Each male flower consists of a small scale or bract, in the axil of which are usually two, sometimes three, rarely five stamens, and still more rarely a larger number.
The female flowers are equally simple, consisting of a bract, from whose axil arises usually a very short stalk, surmounted by two carpels adherent one to the other for their whole length, except that the upper ends of the styles are separated into two stigmas.
I, Branch with male (a) and female (b) inflorescences; 2, bract with three male flowers; 3, bract with three female flowers; 4, infrutescence; 5, fruit.
The lime trees, species of Tilia, are familiar timber trees with sweet-scented, honeyed flowers, which are borne on a common peduncle proceeding from the middle of a long bract.Advertisement
It is this second bract or flowering glume which has been generally called by systematists the " lower pale," and with the " upper pale " was formerly considered to form an outer floral envelope (" calyx," Jussieu; " perianthium," Brown).
The remarkable ovoid involucre of Coix, which becomes of stony hardness, white and polished (then known as " Job's tears," q.v.), is also a modified bract or leaf-sheath.
Rarely the inflorescence consists of very few flowers; thus Lygeum Spartum, the most anomalous of European grasses, has but two or three large uniflorous spikelets, which are fused together at the base, and have no basal glumes, but are enveloped in a large, hooded, spathe-like bract.
Another view is to regard the cone as an inflorescence, each carpellary scale being a bract bearing in its axil a shoot the axis of which has not been developed; the seminiferous scale is believed to represent either a single leaf or a fused pair of leaves belonging to the partially suppressed axillary shoot.
One argument that has been adduced in support of the axillary bud theory is derived from the Palaeozoic type Cordaites, in which each ovule occurs en an axis borne in the axil of a bract.Advertisement
Each cone consists of an axis, on which numerous broad and thin bracts are arranged in regular rows; in the axil of each bract occurs a single flower; a male flower is enclosed by two opposite pairs of leaves, forming a perianth surrounding a central sterile ovule encircled by a ring of stamens united below, but free distally as short filaments, each of which terminates in a trilocular anther.
The overlapping bracts afforded protection to the sporangia, which were borne on sporangiophores springing from the upper surface of the coherent bracts near their origin from the axis; two sporangiophores usually arose from each bract, and sometimes adhered to its upper surface for some distance.
In Cheirostrobus a similar relation of sporangiophores to bracts existed, but here each bract was divided into three segments.
The term bract is properly applied to the leaf from which the primary floral axis, whether simple or branched, arises, while the leaves which arise on the axis between the bract and the outer envelope of the flower are bracteoles or bractlets.
A sheathing bract enclosing one or several flowers is called a spathe.Advertisement
Attached to the peduncle is the bract (h).
About the middle of this axis there is a leaf or bract, from which a secondary floral axis a" is produced, ending in a single flower less advanced than the flower f.
Usually, however, the floral axis, arising from a more or less altered leaf or bract, instead of ending in a solitary flower, is prolonged, and bears numerous bracteoles, from which smaller peduncles are produced, and those again in their turn may be branched in a similar way.
The bract is not, however, the one from which the axis terminating in the flower arises, but is a bract produced upon it, and gives origin in its axil to a new axis, the basal portion FIG.
And finally, we find flowers consisting of a single stamen with a bract.Advertisement
There is thus traced a degradation, as it is called, from a flower with three stamens and three divisions of the calyx, to one with a single bract and a single stamen.
As a rule two sporangiophores belong to each bract.
Each sporangiophore is traversed throughout its length by a vascular bundle connected with that which supplies the subtending bract.
It is thus proved that the sporangiophore is not a mere sporangial stalk, but a distinct organ, in all probability representing a ventral lobe of the subtending bract.
In Sphenophyllum majus, where the cones are less sharply defined, the forked bract bears a group of four sporangia at the bifurcations, but their mode of insertion has not yet been made out.
The plant grows approximately 30 inches tall and produces a fuchsia or purple flower at the end of each bract.
A variety (E. bracteatum) differs in having a bract developed, as E. grandiflorum sometimes has.
The real flowers, located at the base of each bract cluster, should be young and fresh, without any yellow pollen visible.
The flower with its pale is sessile, and is placed in the axil of another bract in such a way that the pale is exactly opposed to it, though at a slightly higher level.
The seeds, or properly fruits, are contained singly in a stony involucre or bract, which does not open until the enclosed seed germinates.