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In this article we will discuss about:- 1. Meaning of Floral Diagram 2. Indication of Floral Diagram 3. How to Draw ?.
Meaning of Floral Diagram:
A floral diagram is a diagram of a cross-section of the flower as it would appear if all floral parts were cut at the same level. It is the ground plan in graphic form to express the arrangement of floral parts as projected in transverse or horizontal plane. It represents young bud as seen in a transverse plane when all floral parts are supposed to be present in their natural arrangement.
The floral parts are represented by concentric circles. The sepals are shown on the outside, petals, stamens and carpels are shown lying within each other. These diagrams usually represents the transverse section of flower and the union and reunion of its parts.
Indication of Floral Diagram:
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The floral diagram furnishes the following informations:
1. Sex and symmetry of the flower.
2. Bracteate or ebracteate nature of flower.
3. Number of floral cycles e.g., tetracyclic or pentacyclic etc.
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4. Number of floral parts in each cycle.
5. Position of floral parts e.g., old sepal is posterior or anterior (e.g. Fabaceae).
6. Aestivation of calyx, corolla or perianth.
7. Cohesion and adhesion of floral parts (e.g., gamopetalous and/or epipetalous nature).
8. Anthers are dithecous or monothecous and introrse or extrorse.
9. Arrangements of stamens, especially in relation to petals, whether there is one whorl or more than one whorl of stamens. Alternipetalous or obdiplostemonous; epipetalous.
10. Staminode if any.
11. Number of carpels, whether free or united, number of locules, number of ovules.
12. Type of placentation.
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13. Cohesion and adhesion of floral parts is indicated by drawing connecting lines between them.
14. Modifications of the sepals or petals e.g. spur or boat shaped.
15. Abortive member by a cross at its assumed position.
16. Position of floral parts towards the mother axis or posterior side (Resupination occurs in orchid flowers).
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17. Bract, when present occupies an anterior and bracteoles lateral positions.
What Is Mother Axis?
Mother Axis is the axis (stem) upon which the flowers are borne. When the flowers are borne laterally upon it, the side of the flower towards the mother axis (or precisely towards the apex of mother axis) is known as the posterior side while the side away from it (the side of the flower towards the bract when it is present) is called as the anterior side.
When the flower is solitary terminal, the flower terminates the mother axis and all sides of it have the same relation to the mother axis. However, when the flower is solitary, axillary the side of flower towards the stem is the posterior side and the side towards the subtending leaf is the anterior side (Fig. 16.1).
What are the Planes of the Flower?
(a) Median Plane:
A vertical plane passing through the mother axis and dividing the flower into two equal halves (and also passing through the middle of bract when one is present) is called the median plane.
(b) Transverse or Lateral Plane:
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A vertical plane dividing the flower into two equal halves and situated at right angle to the median plane is called transverse or lateral plane.
These terms are important in under-standing the floral structure and diagrams, since some flowers described as medianly zygomorphic are laterally zygomorphic.
(c) Diagonal Plane:
A vertical plane dividing the flower into two equal halves and situated at an angle of 45 degrees between the median and the transverse planes is called the diagonal plane. This term is important because in tetramerous flowers, the floral parts are sometimes described to be situated in the diagonal planes, i.e., petals in Brassicaceae.
How to Draw a Floral Diagram?
For making a floral diagram it is best to examine mature floral buds in situ which are at the verge of opening but have not yet opened. Draw a rounded circle to represent the mother axis and the bract below it leaving enough space in between the two to accommodate the floral diagram.
If the flower is ebracteate no bract should be drawn and one can proceed directly to make the floral diagram below the mother axis. Draw transverse sections of bracteoles on the plane on which they are situated, if present.
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Examine the number of sepals, their arrangement in relation to the mother axis and their aestivation. Keeping all these points in view draw transverse sections of sepals below the mother axis or in between the mother axis and the bract when one is present. The same procedure is repeated for the petals (Fig. 16.2).
Do not pluck the floral bud from the mother axis during this operation. However, if it is necessary to pluck the flower bud from the mother axis, mark the posterior or the anterior side depending upon the feasibility by putting an ink dot. In some cases when the flower is plucked from the mother axis, the bract also gets detached with the flower and in this way the anterior side remains automatically labelled.
Now count the number of stamens and the number of whorls in which they are arranged, their position in relation to the petal, the introrse or extrose position of anthers monothecous or dithecous nature of anther and their cohesion and adnation to other floral whorls. Now draw the stamens inner to petals, keeping all these points in view (Fig. 16.2).
Remove the androecium carefully and then study the gynoecium the number of carpels present if the number is odd whether the odd member is towards the posterior side or towards the anterior side; if their number is equal to sepals or petals, they are antisepalous or antipetalous in disposition; whether they are free or united; number of styles, type of placentation and position of the stigmatic lobes whether carinal or commissural.
Now draw a transverse section of the ovary portion of the gynoecium inside the stamens. If there are more than one style and stigma, their position can also be indicated by small circles in contact with the ovary wall.
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In the diagram the sepals and the petals are represented by hollow crescent outlines, the former having pointed apices and shaded with oblique lines while the apices of the latter are round and their cavity is darkly shaded.
Stamens are generally shown by points (staminodes) or as transverse section outline of the anthers, tetralocular for dithecous and bilocular for monothecous anthers. Carpels are represented by the transverse section of their ovaries (Fig. 16.4). The relative size of the sepals, petals or tepals are drawn in the same proportion and aestivation as present in the bud.
Cohesion and adhesion of the floral parts is indicated by drawing connecting lines between them. Modifications of the sepals or petals in the form of a pouch, spur or a boat-shaped structures are shown at the back of the organ in question. Lost or abortive member of a particular whorl is either shown missing or by a cross at its assumed position.
Sometimes the number of nectaries, their position and structure is also represented in a floral diagram (Fig. 15.4). Adnation of members of the different whorls is shown by joining them by radial lines.
In the case of bilabiate calyx and corolla, the two lips are joined by bulging lines.
Resupination occurs in orchid flowers whose stalks twist by 180° so that the posterior side becomes anterior. Bract, when present occupies an anterior and bracteoles lateral positions in a dicotyledonous floral diagram. They are shown like the sepals, either smaller or with little incurved margins.
Inside the floral diagram, the position, shape and number of such structures like the disc and corona etc. can also be incorporated.
