The Dissection, Morphology and Anatomy of a Flower

To describe completely the morphology and anatomy of a flower, it must be fully dissected. Dissection is the process of separating out, piece by piece, the individual structures of a complicated body down to a level at which the eye can see them. With the unaided eye, only coarse dissection can be achieved. Only the comparatively gross anatomy of large bodies can be studied. By the use of magnifying aids of varying strength, finer and finer work can be performed. The student is not debarred from using any aid he may find available. The lowest level of achievement generally acceptable in flower dissection is that made possible by use if a good quality hand – lens (x 10). No flower is so big that a hand lens becomes totally unnecessary and many have some parts at least which are too small to be otherwise clearly distinguishable. A good hand – lens, then, is a necessity and sometimes a microscope (binocular, for preference) can be used with advantage at this higher level of dissection. The student may often find it necessary when confronted with a small, immature gynaecium, to section it and examine it under the low power of the microscope. In conjunction with aids to vision, other instruments are essential and should include fine and coarse forceps, needles, scissors and a sharp razor or scalpel whereby parts may be held, severed, sectioned or generally dismembered.

Complete dissection involves the removal and display in an orderly sequence of all the floral parts so that they may be examined individually. Sectioning of the whole flower in various planes of the parts. The perianth segments and stamens are laid out and the gynaecium sectioned both longitudinally and transversely.

Records of observations made during dissection will be chiefly graphic, i.e., labeled drawings of the whole flower, representative parts of each of the floral whorls where these are separate or of a complete whorl where the parts are joined, and a sagittal or longitudinal section which is generally most useful is that which contains the anterior and posterior of the flower. When a flower develops as a lateral bud on an axis, the side towards the axis is called posterior and the side away, anterior. The terms cannot be applied to a solitary terminal flower. Note carefully that a longitudinal section should include only those faces of structures cut by a razor in slicing a flower in half: only the sagital section include the uncut parts seen in the background.

From the information gained by dissection and illustration the following form of written description may be compiled.

Flower structure and symmetry: Pedicellate or sessile: bract present or absent: unisexual or hermaphrodite: regular or irregular: actinomorphic, zygomorphic or asymmetric: spiral cycle or hemi – cyclic: hypogynous, perigynous or epigynous.

Calyx: Number of parts: free or joined: any special characters such as hairiness, reflexed or otherwise, colour, bearing nectarines or otherwise: variation in form if not all alike.

Corolla: Number of parts: free or joined: any special characters as above.

Androecium: Number of stamens: freely inserted or epipetalous, adelphous or syngenesious: introrse or extrorse.

Gynaecium: Number of carpels: apocarpous or syncarpous: number of loculi: ovule placenta: inferior or superior.

Fruit: Type of fruit and possible dispersal mechanism.

Pollination Mechanism: Special remarks about pollination mechanism from observations in the field or by deduction from flower construction, presence or absence of nectarines, etc.

Further, the flower structure should be represented both diagrammatically and by symbols. The former is the floral diagram and the latter the floral formula.

The floral diagram is constructed on a series of concentric circles, one for each whorl of floral parts. The axis of the inflorescence is represented at the top of the diagram which is then regarded as the posterior position in the flower and the bract of bracts, if any, inserted at the bottom representing the anterior position. On each circle are drawn the various floral segments in their correct relative positions and showing fusions of parts where these occur. One hint may be found useful. The circle representing the gynaecium must be made large enough. It is not easy to draw clearly the detail of a complex ovary in a small space.