The leaf has a broadly sheathing base succeeded by a short stalk bearing the pitcher, which represents a much enlarged midrib with a winglike lamina.
The leaf consists of a central midrib, several cells thick, and two wings, one cell thick.
The midrib has a strong band of stereom above and below.
Or the thallus may have a leaf-like form, the branches from the central threads which form the midrib growing out mainly in one plane and forming a lamina, extended right and left of the midrib.
The centre of the leaf is often occupied by a midrib consisting of several layers of cells.
In the more highly developed series, the mosses, this last division of labor takes the form of the differentiation of special assimilative organs, the leaves, commonly with a midrib containing elongated cells for the ready removal of the products of assimilation; and in the typical forms with a localized absorptive region, a well-developed hydrom in the axis of the plant, as well as similar hydrom strands in the leaf-midribs, are constantly met with.
The stereom of the moss is found mainly in the outer cortex of the stem and in the midrib of the leaf.
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.
In the case of Dionaea muscipula we find a two-lobed lamina, the two lobes being connected by a midrib, which can play the part of a kind of hinge.
Similar turgescence changes, taking place with similar rapidity in the midrib of the leaf of Dionaea, explainthe closing of the lobes upon their hinge.
When uniformly damped, the leaves are separately opened out and smoothed, the midrib, if not already removed, is torn out, except when " bird'seye " cut is to be made, in which mixture the midrib gives the peculiar " bird's-eye " appearance.
The effect of the light falling upon them is to produce along the midrib of each a number of short white streaks of light, which contrast most strongly with the shadows cast by the leaves themselves, and with the general twilight gloom of the forest.
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.
A leaf with only a single midrib is said to be unicostate and the venation is described as pinnate or feather-veined.
4), in place of there being only a single midrib there are several large veins (ribs) of nearly equal size, which diverge from the point where the blade joins the petiole or stem, giving off lateral veins.
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.
8), it is cleft; when the divisions extend nearly to the base or to the midrib the leaf is partite.
Besides the midrib there are two intra-marginal ribs which converge to the apex.
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.
The midrib, or petiole, has thus the appearance of a branch with FIG.
19), the leaf is unequally pinnate (imparipinnate); when the leaflets or pinnae are placed alternately on either side of the midrib, and not directly opposite to each other, the leaf is alternately pinnate; and when the pinnae are of different sizes, the leaf is interruptedly pinnate.
Some petioles are long, slender and sensitive to contact, and function as tendrils by means of which the plant climbs; as in the l,' nasturtiums (Tropaeolum), clematis and c in others; and in compound leaves the midrib and some of the leaflets may similarly be transformed into tendrils, as in the pea and vetch.
And others, the midrib of the leaf ends in a tendril.
A very finely made copper dagger (60) with deep midrib is dated to between 55 and 60 S.D.
In Iridaea the thallus is an entire lamina; in Callophyllis a lobed lamina; in Delesseria it is provided with midrib and veins, simulating the appearance of a leaf of the higher plants; in Constantinea the axis remains cylindrical, and the lateral branches assume the form of leaves.
In weight, with the midrib of the leaf they are wrapped in forming a median line on the surface.
The venation is strictly parallel, the midrib usually strong, and the other ribs more slender.
In dry-country grasses the blades are often folded on the midrib, or rolled up. The rolling is effected by bands of large wedge-shaped cells - motor-cells - between the nerves, the loss of turgescence by which, as the air dries, causes the blade to curl towards the face on which they occur.
The flowering glume has generally a more or less boat-shaped form, is of firm consistence, and possesses a well-marked central midrib and frequently several lateral ones.
14, 7), which corresponds to the midrib of the carpel.
The Cyas type of frond, except as regards the presence of a midrib in each pinna, characterizes the cycads generally, except Bowenia and Stangeria.
Nageia) a canal occurs below each vein; in Tsuga, Torreya, Cephalotaxus, Sequoia, &c., a single canal occurs below the midrib; in Larix, Abies, &c., two canals run through the leaf parallel to the margins.
The sori are borne on the under surface of the pinnae, usually in a single row on either side of the midrib, but in Kaulfussia dotted over the expanded lamina.
In 1843 a German bee-keeper, Krechner by name, conceived the idea of first dipping fine linen into molten wax, then pressing the sheets so made between rollers, and thus forming a waxen midrib on which the bees would build their combs.
These sheets were readily accepted by the bees, and afterwards plates cast from metal were employed, with so good a result as to give to the bees as perfect a midrib as that of natural comb with the deep cell walls cut away.
Weed, a skilful American machinist, who, after some years of strenuous effort, succeeded in devising and perfecting special rollers and dies, by the use of which foundation was produced with a midrib so thin as to compare favourably with natural comb built by the bees.
Form of Comb Midrib (five cells to the inch).
In it no fruit is produced, and the pistil consists merely of sessile leaves, the limb of each being green and folded, with a narrow prolongation upwards, as if from the midrib, and ending in a thickened portion.
In the Lower Carboniferous of Scotland Mr Kidston has found several specimens of a large dichotomous thallus, with a very distinct midrib; the specimens, referred to the provisional genus Thallites, much resemble the larger thalloid Liverworts.
The change in the character of the vegetation was con which have generally been regarded as the fronds of ferns characterized by a central midrib giving off lateral veins which repeatedly anastomose and form a network, like that in the leaves of Antrophyum, an existing member of the Polypodiaceae.
Associated with Glossopteris occurs another fern, Gangamopteris, usually recognized by the absence of a well marked midrib, though this character does not always afford a satisfactory distinguishing feature.
Professor Nathorst, as the result of a more recent examination of Heer's specimen, found that the segments of the frond are characterized by the presence of two parallel veins instead of a single midrib, with a row of stomata between them; for this type of Cycadean leaf he proposed the generic name Pseudocycas.
They are shrubby plants climbing over surrounding vegetation by means of tendrillike prolongations of the midrib of the leaf beyond the leaf-tip.