Morphology of Flowering Plants Test - 3

In epigynous flowers, the thalamus is hollowed out in the form of a flask but its internal wall is fused with wall of the ovary. Only the style and stigmaof the pistal are obervable from the upper side. Other floral organs are borne at the top of ovary. The ovary or gynoecium is said to be inferior while other floral organs are superior, e.g., apple, sunflower, cucumber, etc.

There are three forms of thalamus in regard to the insertion of pistil and androperianth or other floral organs..
(i) Hpogyny - When the sepals, petals and stamens are successively and separately inserted below the ovary in the flowers, the condition is known to be hypogyny and the ovary is said to be ruperious. Such flowers are called hypogyous as in mustard,china rose and brinjal.
(ii) Epigyny - When the sepals, petals and stamens are successively and separately inserted above the ovary in the flower, the condition is descried as epigymy. The ovary in this situation is said to be inferior. Such flowers are termed epigynous, e.g., guave, cucumber.
(iii) perigymy - When the sepals, petals and stamens are inserted at the same plane as the ovary, the condition is known as perigyny. The ovary in such condition is half superior, sub-inferior or partially inderior ovary. Such flowers are called perigynous, e.g., rose, pea.

When stamens are attached to the perianth, they are known as epiphyllous, e.g., Asparagus, lily.

In hypogynous condition of flowers, the thalamus is convex or conical. Gynoecium occupies the topmost (superior) position at the thalamus and other parts of flower are borne successively below. Androperianth or other floral organs are inferior, e.g, Hibiscus rosa sinensis, Ranunculus, etc.

Parietal pacentation occurs in the members of family brassic aceae. In Brassica ovary is unilocular but modification occurs and it becomes bilocular. A false septum called replum develops between the two parietal placentae in mustard and other memebrs of family.

The arrangement of ovules within the ovary is known as placentation. The placentation are of different type namely, marginal, axile, parietal, basal, central and free central. In marginal placemation the placenta forms a ridge along the ventral suture of the ovary and the ovules are borne on this ridge forming two rows, e.g. pea. When the placenta is axial and the ovules are attached to it in a multilocular ovary, the placentation is saidd to be axile, e.g., China rose, tomato and lemon In parietal placentation, the ovules develop on the inner wall of the ovary or on peripheral part. Ovary is one -chambered but it becomes two chambered due to the formation of false septum, e.g., mustard. When the ovules are borne on central axis and septa are absent, as in Primrose, the placentation is called free central In basal placentation, the placenta develops at the base of obary and a single ovule is attached to it, e.g., sunflower, marigold.

A - Twisted
B - Imbricate
C - Valvate
D - Vexillary

In perigynous condition of a filower, the gynoecium is situated in the centre and other floral parts are located on the rim of the thalamus almost at the same level. Ovary is said to be half-inferior, e g. Rosa (Flask-shaped thalamus) Prunus (Cup-shaped thalamus).

Option (a) represents placentation as seen in China rose. It is axile type of placentation, which occurs in syncarpous pistils. Ovary is partitioned into 2 or more chambers. Placentae occur in the central region where the septa meet so that an axile column bearing ovules is formed. In China rose, ovary is pentalocular.

Some flowers (member of family Fabaceae) show diadeIphous kind of arrangement i.e., (9) + 1 o r (5  + (5) , in which fusion of filaments produces two groups. In cucurbits, synandrous condition of stamens is present in which stamens are fused by both their filaments as well as anthers.

In papilionaceous corolla , five unequal petals are arranged like a butterfly. The posterior large bilobed petal is called standard or vexillum and it overlaps two smaller lateral petals called wings/alae. The latter in turn overlap the two anterior petals which are fused by the upper anterior margins to form a boat-shaped structure called keel or carina.

In valvate aestivation, margins of the adjacent petals touch each other but without overlapping e.g., corolla of Brassica, Calotropis.

In vexillary/descending imbricate aestivation, the posterior petal overlaps the two lateral petals and the latter overlap the two anterior petals. It is also called papilionaceous corolla and found in members of family Papilionaceae.

In family Asteraceae, anthers are syngenesious (synantherous) in which stamens are fused together at their edges by anthers only, forming a ring around the gynoecium.
The filaments are free, e.g., Sunflower.

The anothers which contain only one another lobe are called monothecous anthers. Monothecours anthers are bisporangiate (contain two pollen sacs), as in family Malvaceae.