The anatomical construction of these plants presents many peculiarities which have given rise to discussion as to the allocation of the order among the dicotyledons or among the monocotyledons, the general balance of opinion being in favour of the former view.
The embryo consists of an axis bearing one (Monocotyledons) or two (Dicotyledons) cotyledons, which protect the stem bud (plumule) of the future plant, and ending below in a radicle.
The monocotyledons, one of the primary divisions of angiosperms, typically possess large Monocoty- leaves with broad Iedonous sheathing bases containType.
The periblem, one cell thick at the apex, produces the cortex, to which the piliferous layer belongs in Monocotyledons; and the plerome, which is nearly always sharply separated from the periblem, gives rise to the vascular cylinder.
In most of the existing Pteridophytes, in the Monocotyledons and in annual plants among the Dicotyledons, there is n further growth of much structural importance in the ~ d ~
An ordinary cambium is scarcely ever found in the Monocotyledons, but in certain woody forms a secondary meristem is formed outside the primary bundles, and gives rise externally to a little secondary cortex, and internally to a secondary parenchyma in which are developed numerous zones of additional bundles, usually of concentric structure, with phloem surrounded by xylem.
It has since been shown by other observers that this double fertilization Occurs in many other Angiosperms, both Dicotyledons and Monocotyledons, so that it is probably of general occurrence throughout the group (see ANGIOSPERMS).
TROPICAL REGI0N.This is characterized by the presence of gigantic Monocotyledons, palms, Musaceae and bamboos, and of evergreen polypetalous trees and figs.
The remains of palms (Sabctl and Nipa) as well as of other large-leaved Monocotyledons are preserved.
Other characteristic features of the flora are the abundance of Compositae, Asclepiadeae, and petaloid Monocotyledons generally, but especially Orchideae (terrestrial species predominating) and Iridaceae.
The parts of the flower are most frequently arranged in fives, or multiples of fives; for instance, a common arrangement is as follows, - five sepals, succeeded by five petals, ten stamens in two sets of five, and five or fewer carpels; an arrangement in fours is less frequent, while the arrangement in threes, so common in monocotyledons, is rare in dicotyledons.
The flowers of all orchids, though extremely diverse within certain limits, and although superficially very different from those of other monocotyledons, are ° 1' all formed upon one common plan, which is only a modification of that observable in such flowers as those of the narcissus s ate/ S `?
LILIACEAE, in botany, a natural order of Monocotyledons belonging to the series Liliiflorae, and generally regarded as representing the typical order of Monocotyledons.
JUNCACEAE (rush family), in botany, a natural order of flowering plants belonging to the series Liliiflorae of the class Monocotyledons, containing about two hundred species in seven genera, widely distributed in temperate and cold regions.
AROIDEAE (Arum family), a large and wide-spread botanical order of Monocotyledons containing about 1000 species in 105 genera.
The structure of the flower represents the simple type of monocotyledons, consisting of two whorls of petals, of three free parts each, six free stamens, and a consolidated pistil of three carpels, ripening into a three-valved capsule containing many winged seeds.
Many monocotyledons do well in peat, even if they do not absolutely require it.
In some Monocotyledons, ordinarily in Chlorophytum, and exceptionally in Phalaenopsis and others, new plants arise on the flower stems.
It not unfrequently happens, especially amongst Monocotyledons, that after growth at the apex has ceased, it is continued at the base of the leaf, and in this way the length may be much increased.
The leaves of Monocotyledons have generally this kind of venation, while reticulated venation most usually occurs amongst Dicotyledons.
Such arrangements as 2, 3 ands are common in Monocotyledons, as in grasses, sedges and lilies.
In the smaller group, the Monocotyledons, the bundles are more numerous in the young stem and scattered through the ground tissue.
As in Gymnosperms, branching is monopodial; dichotomy or the forking of the growing point into two equivalent branches which replace the main stem, is absent both in the case able variety in form (see Leaf), but are generally small in comparison with the size of the plant; exceptions occur in some Monocotyledons, e.g.
In many Dicotyledons and most Monocotyledons, the primary root soon perishes, and its place is taken by adventitious roots developed from the stem.
This remarkable double fertilization as it has been called, although only recently discovered, has been proved to take place in widely-separated families, and both in Monocotyledons and Dicotyledons, and there is every probability that, perhaps with variations, it is the normal process in Angiosperms. After impregnation the fertilized oosphere immediately surrounds itself with a cell-wall and becomes the oospore which by a process of growth forms the embryo of the new plant.
In many Monocotyledons the terminal cell forms the cotyledonary portion alone of the shoot of the embryo, its axial part and the root being derived from the adjacent cell; the cotyledon is thus a terminal structure and the apex of the primary stem a lateral one - a condition in marked contrast with that of the Dicotyledons.
In some Monocotyledons, Pistil and macrosporangium, is very similar to the process in Fertiliza- to the opening of the micropyle, into which the pollen- tion.
We readily recognize in them nowadays the natural classes of Dicotyledons and Monocotyledons distinguished alike in vegetative and in reproductive construction, yet showing remarkable parallel sequences in development; and we see that the Dicotyledons are the more advanced and show the greater capacity for further progressive evolution.
But there is no sound basis for the assumption that the Dicotyledons are derived from Monocotyledons; indeed, the palaeontological evidence seems to point to the Dicotyledons being the older.
This, however, does not entitle us to assume the origin of Monocotyledons from Dicotyledons, although there is manifestly a temptation to connect helobic forms of the former with ranal ones of the latter.
In Monocotyledons a similar advance from hypogyny to epigyny is observed, and from the dorsiventral to the radial type of flower.
Well-defined polypetalous and gamopetalous genera sometimes occur in the same order, and even Monocotyledons and Dicotyledons are classed together where they have some .striking physiological character in common.
The orders are carefully characterized, and those of Angiosperms are grouped in fourteen classes under the two main divisions Monocotyledons and Dicotyledons.
Monocotyledons in seven series.
The seven series of Monocotyledons represent a sequence beginning with the most complicated epigynous orders, such as Orchideae and Scitamineae, and passing through the petaloid hypogynous orders (series Coronarieae) of which Liliaceae is the representative to Juncaceae and the palms (series Calycinae) where the perianth Ioses its petaloid character and thence to the Aroids, screw-pines and albuminous Dicotyledons the cotyledons act as the absorbents of the reserve-food of the seed and are commonly brought above ground (epigeal), either withdrawn from the seed-coat or carrying it upon them, and then they serve as the first green organs of the plant.
In albuminous Monocotyledons the cotyledon itself, probably in consequence of its terminal position, is commonly the agent by which the embryo is thrust out of the seed, and it may function solely as a feeder, its extremity developing as a sucker through which the endosperm is absorbed, or it may become the first green organ, the terminal sucker dropping off with the seed-coat when the endosperm is exhausted.
Exalbuminous Monocotyledons are either hydrophytes or strongly hygrophilous plants and have often peculiar features in germination.
It is based upon the fact that the histological differentiation of the epidermis of their root is that generally characteristic of Monocotyledons, whilst they have two cotyledons - the old view of the epiblast as a second cotyledon in Gramineae being adopted.
IRIDACEAE (the iris family), in botany, a natural order of flowering plants belonging to the series Liliiflorae of the class Monocotyledons, containing about Boo species in 57 genera, and widely distributed in temperate and tropical regions.
BROMELIACEAE, in botany, a natural order of Monocotyledons, confined to tropical and sub-tropical America.
(Sedge family), Juncaceae (Rush family), and some other monocotyledons with inconspicuous flowers.
In internal structure grass-culms, save in being hollow, conform to that usual in monocotyledons; the vascular bundles run parallel in the internodes, but a horizontal interlacement occurs at the nodes.
The pale is now generally considered to represent the single bracteole, characteristic of Monocotyledons, the binerved structure being the result of the pressure of the axis of the spikelet during the development of the pale, as in Iris and others.
It was the English botanist Robert Brown who first recognized this important distinguishing feature in conifers and cycads in 1825; he established the gymnospermy of these seed-bearing classes as distinct from the angiospermy of the monocotyledons and dicotyledons.
IiXtr t ta, a water-plant mentioned by Dioscorides), in botany, a natural order of monocotyledons belonging to the series Helobieae, and represented in Britain by the water plantain, Alisma Plantago, the arrow-head, Sagittaria, the star-fruit, Damasonium, and flowering rush, Butomus (from the Gr.
SiK-rvov, a net, and the termination -rye pis, produced), a botanical name proposed by John Lindley for a class including certain families of Monocotyledons which have net-veined leaves.