Word Finder - petiole

definition

The stalk of a leaf, attaching the blade to the stem.

synonyms

• pedicel

definition

(insect anatomy) A narrow or constricted segment of the body of an insect; especially, the metasomal segment of certain Hymenoptera, such as wasps.

synonyms

• pedicel

definition

The stalk at the base of the nest of the paper wasp.

The petiole varies in length, being usually shorter than the lamina, but sometimes much longer.

This tissue remains living and is usually formed quiti early, just below the epidermis, where it provides the first periphera support for a still growing stem or petiole.

In general, the petiole is more or less rounded in its form, the upper surface being flattened or grooved.

In the larger veins of the leaf especially in the midrib, in the petiole, and in the young stem, a1 extremely frequent type of mechanical tissue is collenchyma.

A layer of cork is regularly formed in most Phanerogams across the base of the petiole before leaf fall, so as to cover the wound caused by the separation of the leaf from the stem.

In the erect position of the leaf the lower side has its cells extremely turgid, and the pulvinus thus forms a cushion, holding up the petiole.

The petiole is inserted a little above the base, and hence the leaf is called peltate or shieldlike.

In this way two marked forms of leaf are produced - (I) Simple form, in which the segmentation, however deeply it extends into the lamina, does not separate portions of the lamina which become articulated with the midrib or petiole; and (2) Compound form, where portions of the lamina are separated as detached leaflets, which become articulated with the midrib or petiole.

It is a pinnatifid leaf, with the divisions pointing towards the petiole and a large triangular apex.

The midrib, or petiole, has thus the appearance of a branch with FIG.

The petiole or leaf-stalk is the part which unites the limb or blade of the leaf to the stem.

In some Australian acacias, and in some species of Oxalis and Bupleurum, the petiole is flattened in a vertical direction, the vascular bundles separating immediately after quitting the stem and running nearly parallel from base to apex.

On the same acacia there occur leaves with the petiole and lamina perfect; others having the petiole slightly expanded or winged, and the lamina imperfectly developed; and others in which there is no lamina, and the petiole becomes large and broad.

They are not usually of the same form as the ordinary foliage leaves of the plant, from which they are distinguished by their lateral position at the base of the petiole.

In Lathyrus Aphaca and some other plants the true pinnate leaves are abortive, the petiole forms a tendril, and the stipules alone are developed, perform ing the office of leaves.

In the case of alternate leaves, the stipules at the base of each leaf are sometimes united to the petiole and to each other, so as to form an adnate, adherent or petiolary stipule, as in the rose, or an axillary stipule, as in Houttuynia cordata.

In Nymphaea micrantha buds appear at the upper part of the petiole.

Ovular characters determine the grouping in the Dicotyledons, van Tieghem supporting the view that the integument, the outer if there be two, is the lamina of a leaf of which the funicle is the petiole, whilst the nucellus is an outgrowth of this leaf, and the inner integument, if present, an indusium.

The chief modifications are the articulation of the deciduous blade on to the sheath, which occurs in all the Bambuseae (except Planotia) and in Spartina stricta; and the interposition of a petiole between the sheath and the blade, as in bamboos, Leptaspis, Pharus, Pariana, Lophatherum and others.

Culm woody, at any rate at the base, leaf-blade jointed to the sheath, often with a short, slender petiole.

Similarly, the dead fronds fall off,leaving a ragged petiole, which is afterwards separated from the stem by an abscess-layer a short distance above the base.

The distal ends of these girdles give off several branches, which traverse the petiole and rachis as numerous collateral bundles.

In a bundle examined in the basal portion of a leaf the bulk of the xylem is found to be centrifugal in position, but internally to the protoxylem there is a group of centripetal tracheids; higher up in the petiole the xylem is mainly centripetal, the centrifugal wood being represented by a small arc of tracheids external to the protoxylem and separated from it by a few parenchymatous elements.

The morphology of the female flowers has been variously interpreted by botanists; the peduncle bearing the ovules has been described as homologous with the petiole of a foliage-leaf and as a shoot-structure, the collar-like envelope at the base of the ovules being referred to as a second integument or arillus, or as the representative of a carpel.

A petal often consists of two portions - the lower narrow, resembling the petiole of a leaf, and called the unguis or claw; the upper broader, like the blade of a leaf, and called the lamina or limb.

The petiole was usually traversed by a single vascular bundle, hippocrepiform in section - a marked point of difference from the more complex petioles of recent Marattiaceae.

The single vascular bundle which traversed the petiole and its branches was concentric, the leaves resembling those of Ferns in structure as well as in habit.

Similarly, the genus Sagenopteris, characterized by a habit like that of Marsilia, and represented by fronds consisting of a few spreading broadly oval or narrow segments, with anastomosing veins, borne on the apex of a common petiole, is abundant in rocks ranging from the Rhaetic to the Wealden, but has not so far been satisfactorily placed.

Nevertheless they sufficed to attract the eye, when the whole petiole was viewed as a transparent object beneath the microscope.

The culms are brown when ripe; the leaf-sheaths are hairy, and the petiole of the leaf is yellow.

In habit it closely resembles C. plantaginea, forming a comparatively compact mass, increasing by short side growths; the leaves are intermediate, narrower than those of C. plantaginea, but not showing the distinct petiole of C. polyrrhiza.

The leaves are long and narrowed into a petiole, and are softly hairy on both surfaces.

In the petiole these strands may increase in number by branching, and thotigh usually reducible to the outline of the primitive horseshoe, more or less elaborated, they may in some of the complex polycylic dictyostelic types (Marattiaceae) be arranged in several concentric circles, thus imitating the arrangement of strands formed in the stem.

The evolution of the vascular structure of the petiole in the higher ferns is strikingly parallel with that of the stem, except in some few special cases.

The bundle-system is of course continuous with that of the petiole and stem.

Bassett, 3 is the petiole, and its terminal tuft of woolly hairs the enormously developed pubescence of the young oak-leaf.

The leaves of the foxglove, gathered from wild plants when about two-thirds of their flowers are expanded, deprived usually of the petiole and the thicker part of the midrib, and dried, constitute the drug digitalis or digitalis folia of the Pharmacopoeia.

The part of the leaf next the petiole or the axis is the base, while the opposite extremity is the apex.

The laminar portion of a leaf is occasionally articulated with the petiole, as in the orange, and a joint at times exists between the vaginal or stipulary portion and the petiole.

Compound leaves are those in which the divisions extend to the midrib or petiole, and the sepa rated portions become each arti culated with it, and receive the name of leaflets.