Rubra, has thin large leaves on long petioles, the lobes very long and acute, the points almost bristly; they are pink when they first expand in spring, but become of a bright glossy green when full-grown; in autumn they change to the deep purplered which gives the tree its name.
The leaves are broader than in most willows, and are generally either deltoid or ovate in shape, often cordate at the base, and frequently with slender petioles vertically flattened.
In diameter, and with the shoots or young branches more or less angular; the glossy deltoid leaves are sharply pointed, somewhat cordate at the base, and with flattened petioles; the fertile catkins ripen about the middle of June, when their opening capsules discharge the cottony seeds which have given the tree its common western name; in New England it is sometimes called the "river poplar."
The true balsam poplar, or tacamahac, P. balsamifera, abundant in most parts of Canada and the northern States, is a tree of rather large growth, often of somewhat fastigiate habit, with round shoots and oblong-ovate sharp-pointed leaves, the base never cordate, the petioles round, and the disk deep glossy green above but somewhat downy below.
10 The galls of examples of the last family are common objects on lime-leaves, and on the petioles of the poplar.
In some cases leaves, as in Iris, or leaf-like petioles, as in Australian acacias and eucalypti, have their plane of expansion parallel to the axis of the shoot, there is then no distinction into an upper and a lower face, but the two sides are developed alike; or the leaf may have a cylindrical or polyhedral form, as in mesembryanthemum.
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.
Pitchers are formed either by petioles or by laminae, and they are composed of one or more leaves.
The roundish leaves, toothed on the margin, are slightly downy when young, but afterwards smooth, dark green on the upper and greyish green on the lower surface; the long slender petioles, much flattened towards the outer end, allow of free lateral motion by the lightest breeze, giving the foliage its well-known tremulous character.
A feature of interest in connexion with the phylogeny of cycads is the presence of long hairs clothing the scale-leaves, and forming a cap on the summit of the stem-apex or attached to the bases of petioles; on some fossil cycadean plants these outgrowths have the form of scales, and are identical in structure with the ramenta (paleae) of the majority of ferns.
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 petioles have a somewhat complex structure, the bundle often having, in transverse section, the form of an H; it has been proposed to subdivide the genus on the details of the petiolar structure.
The spirally arranged petioles (Myeloxylon) were of great size, and their decurrent bases clothed the surface of the stem; their (From structure is closely similar to that Studies.) of recent Cycadean petioles; in FIG.
The lozenge-shaped areas external to the axis of the stem represent the sections of petioles, some of which are shown in fig.
Cycads, but the ramenta, instead of having the form of long unicellular hairs like those on the petioles and bud-scales of existing species are exactly like the paleae or ramental scales characteristic of the majority of ferns.
A number of hairy linear bracts enclose the whole; internal to these occur 12 to 20 crowded pinnate leaves (sporophylls), with their apical portions bent over towards the axis of the flower, the bases of the petioles being fused laterally into a disk surrounding the base of the conical receptacle.