There are a large number of varieties, differing chiefly in the form and division of the pinnae; var.
Cambricum (originally found in Wales) has the pinnae themselves deeply cut into narrow segments; var.
Cristatum is a handsome variety with fronds forking at the apex and the tips of all the pinnae crested and curled.
Long, including the stalk; it is characterized by having the lower pinnae of the frond deflexed; it is generally distributed in Britain, though not common.
In these animals the eyeball and the fur of the body are unpigmented, but the tips of the ear pinnae and extremities of the fore and hind limbs, together with the tail, are marked by more or less well defined colour.
In others (Polystichum angulare proliferum) the stipes below and the rachis amongst the pinnae develop buds, which are often numerous and crowded.
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.
When the division is carried into the second degree, and the pinnae of a compound leaf are themselves pinnately compound, a bipinnate leaf is formed.
There are nine pairs of shortly-stalked leaflets (foliola, pinnae), and an odd one at the extremity.
In Leguminous plants (the pea tribe) the pinnae are frequently modified to form tendrils, as in Lathyrus Aphaca, in which the stipules perform the function of true leaves.
I) on the branched or unbranched stem; (b) the growth of the main stem through the female flower; (c) the presence of a prominent single vein in the linear pinnae; (d) the structure of the female flower, which is peculiar in not having the form of a cone, but consists of numerous independent carpels, each of which bears two or more lateral ovules.
- The pinnae are traversed by several parallel veins.
The various genera are distinguished from one another by the shape and manner of attachment of the pinnae, the form of the carpellary scales, and to some extent by anatomical characters.
In rare cases the pinnae of cycads are lobed or branched: in Dioon spinulosum (Central America) the margin of the segments bears numerous spinous processes; in some species of Encephalartos, e.g.
An interesting species of Cycas, C.Micholitzua, has recently been described by Sir William Thiselton-Dyer from Annam, where it was collected by one of Messrs Sanders & Son's collectors, in which the pinnae instead of being of the usual simple type are FIG.
The young leaves arise on the stem-apex as conical protuberances with winged borders, on which the pinnae appear as rounded humps, usually in basipetal order; the scale-leaves in their young condition resemble fronds, but the lamina remains undeveloped.
The first leaves borne on the seedling axis are often scalelike, and these are followed by two or more larger laminae, which foreshadow the pinnae of the adult frond.
Finally, in the pinnae of the frond the centrifugal xylem may disappear, the protoxylem being now exarch in position and abutting on the phloem.
The long linear leaves of some species of Podocarpus, in which the lamina is traversed by a single vein, recall the pinnae of Cycas; the branches of some Dacrydiums and other forms closely resemble those of lycopods; these superficial resemblances, both between different genera of conifers and between conifers and other plants, coupled with the usual occurrence of fossil coniferous twigs without cones attached to them, render the determination of extinct types a very unsatisfactory and frequently an impossible task.
There are always eight tentacles, which are hollow and fringed on their sides, with hollow projections or pinnae; and always eight mesenteries, all of which are complete, i.e.
8), the colony looks like a feather having a stem divisible into an upper moiety or rachis, bearing lateral central leaflets (pinnae), and a lower peduncle, which is sterile and imbedded in sand or mud.
The pinnae are formed by the elongated autozooids, whose proximal portions are fused together to form a leaf-like expansion, from the upper edge of which the distal extremities of the zooids project.
The siphonozooids are very numerous and lie between the bases of the pinnae on the pararachides; they extend also on the prorachidial and metarachidial surfaces.
The pinnae, except in a few filmy forms, are thick; in Kaulfussia large pores derived from stomata occur in the epidermis.
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 Osmunda the region of the leaf which bears the sporangia has its lamina little developed; the leaf thus bears sterile and fertile pinnae, or, as in 0.
The sporangia are borne singly or in sori of two or three on the margin or under surface of leaves, the fertile pinnae of which differ more or less from the sterile segments.
The sori ale borne on the under surface of the pinnae, in the D (From Strasburger's Lehrbuch der Botanik.) FIG.
Or more broad; the tops of the fronds are fertile, the fertile pinnae being cylindrical and densely covered with the spore-cases, giving the appearance of a dense panicle of flowers, whence the plant is known as the flowering fern.
There are various cultivated forms - cristata has the ends of the fronds and the pinnae finely crested, and corymbifera has curiously forked and crested fronds.
It is, however, probable that a considerable group of true Ferns, allied to Marattiaceae, existed in Palaeozoic times, side by side with simpler forms. In one respect the fronds of many Palaeozoic Ferns and Pteridosperms were peculiar, namely, in the presence on their rachis, and at the base of their pinnae, of anomalous leaflets, often totally different in form and venation from the ordinary pinnules.
In many fern-like plants of this period the fronds were dimorphic, the fertile leaves or pinnae having a form quite different from that of the vegetative portions.
The magnificent Devonian Fern Archaeopteris hibernica, with a somewhat Adiantiform habit, bore special fertile pinnae; the fructification is still imperfectly understood, but the presence of stipules, observed by Kidston, has been adduced in support of Marattiaceous affinities.
It is characteristic of Zygopteris and its near allies that two rows of pinnae were borne on each side of the rachis, at least in the fertile fronds.
Fertilis, from the Pottsville beds (Millstone Grit) of West Virginia, the rhomboidal seeds, flattened and winged like those of Cordaiteae, are borne terminally on the lateral pinnae of a frond, which elsewhere bears the characteristic cuneiform leaflets.
As examples of these doubtful forms may be mentioned Thinnfeldia, characteristic of Rhaetic and Lower Jurassic rocks; Dichopteris, represented by some exceptionally fine Jurassic specimens, described by Zigno, from Italy; and Ctenis, a genus chiefly from Jurassic beds, founded on pinnate fronds like those of Zamia and other Cycads, with linear pinnae characterized by anastomosing veins.
5, A), a characteristic Yorkshire fossil of Jurassic age, which in the form of the frond, bearing broad and relatively short pinnae, exhibits a striking agreement with the sterile portions of the fronds of Aneimia rotundifolia, a member of the fern family Schizaeaceae.
It has been found useful in some cases to examine microscopically the thin film of coal that often covers the pinnae of fossil fronds, in order to determine the form of the epidermal cells which may be preserved in the carbonized cuticle; rectilinear epidermal cell-walls are usually considered characteristic of Cycads, while cells with undulating walls are more likely to belong to Ferns.
This type is distinguished by its large bipinnate fronds bearing long and narrow pinnae with close-set pinnules, characterized by the anastomosing secondary veins.
Ctenis has been incorrectly placed among the ferns by some authors, on account of the occurrence of supposed sporangia on its pinnae; but there is reason to believe that these so-called sporangia are probably nothing more than prominent papillose cells of the epidermis.
12) is usually considered to be a Cycad, but the broad pinnae (or leaves) and their arrangement on the axis suggests a possible relationship with the southern coniferous genus Agathis, represented by the Kauri pine and other recent species.
The considerable variation in the size of the pinnae of Podozamites, as represented by species from the Jurassic rocks in the Arctic regions and various European localities, recalls the variation in length and breadth of the leaves of Agathis.