Anthers of flower – Attachment, Dehiscence & Forms of Anther
Anthers or Microsporangia:
Anthers of flower are composed of two anther sacs or lobes separated by a tissue called connective — each lobe or sac consists of two microsporangia separated by a septum.
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So in an anther there are altogether four microsporangia. Hence a fully developed anther shows quadrilocular structure.
In majority of the cases anthers appear bilocular in structure due to absorption of septa separating the two sporangia of anther sac or lobe. Unilocular or one-celled anther, as seen in Malvaceae, arises either due to (a) abortion of one anther lobe and the dissolution of the septum between the two sporangia, or (b) due to the destruction of partition wall (connective) of the two lobes as well as of the septa between the sporangia of each lobe.
Anthers may be introrse (when grooved anther-face, particularly the line of dehiscence, is directed towards the gynoecium or centre of the flower) or extrorse (when grooved anther-face is directed towards petals).
A. ATTACHMENT OF ANTHER TO THE FILAMENT
There are four modes of attachment as follows:
(a) Innate or Basifixed — When the filament is firmly attached to the base of the anther e.g. species of Carex (Cyperaceae), Solanum (Solanaceae), members of Cruciferae etc.
(b) Adnate — When the filament or its continuation, the connective, is attached to the back of anther throughout the whole length, e.g, Nymphaea sp. (Nymphaeaceae), Magnolia sp. (Magnoliaceae) etc.
(c) Dorsifixed — When the filament is firmly attached to the back of the anther, e.g. Passiflora sp. (Passifloraceae), Sesbania sp. (Papilionaceae) etc.
(d) Versatile anther — When filament is attached at a point near the middle of the back of the connective in such a way that the anther can swing free in air, e.g. in some members of Liliaceae, Amaryllidaceae, all members of Gramineae etc.
Also Read: Stamens of Flower – Definition, Parts & Types (With Diagram)
B. DEHISCENCE OF ANTHERS
Anther lobes i.e. microsporangia of angiosperms dehisce or burst in order to enable the pollen grains to come out.
The dehiscence may be :
(1) Transverse — It is seen in one-called anther of Malvaceae, Lemna sp. (Lemnaceae) etc. ; due to horizontal placing of anther lobe the dehiscence appears to be transversely slit like the lid of a box.
(2) Apical or Porous — In Solanum sp. the dehiscence of anther lobes takes place through apical pores.
(3) Valvular — When dehiscence or bursting of anther lobes is effected by means of trapdoor-like flappy valves as in Berberis sp. (Berberidaceae), Litsea sp., Cinnamomum zeylanicum (Lauraceae) etc.
(4) Longitudinal — This is very common, here the anther lobe splits lengthwise from base to apex along the line of suture, e.g. Vitis vinifera (Vitaceae), Datura sp. (Solanaceae) etc.
C. FORMS OF ANTHER LOBES
Anther lobes may be :
(1) Linear — the anther lobes are long and narrow, as in Acalypha sp. (Euphorbiaceae).
(2) Round or Oval as in Mercurialis annua (Euphorbiaceae).
(3) Appendiculate — where the anther lobes are provided with appendages of different kinds e.g. flattened leafy in Erica cinerea (Ericaceae), pointed in Vaccinium sp. (Vacciniaceae), Justicea sp. (Acanthaceae) etc.
(4) Reniform i.e. kidney-shaped as in members of Malvaceae.
(5) Sagittate anther i.e. arrow-shaped e.g. in Lochnera (Vinca) sp. (Apocynaceae).
(6) Sinuous — Lobes convoluted forming ‘S’-shaped structure, e.g. in members of Cucurbitaceae.
(7) Filamentous — When the lobes are thread-like, e.g. Zostera sp. (Potamogetonaceae).
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