Evidences regarding flower as a modified shoot

Flower is the reproductive part of the plant. It is the most conspicuous structure of the angiosperm plants.

Morphologically, it represents a short and compact branch, the growth of which is ceased. It develops from the floral bud. It is regarded as a metamorphosed shoot meant essentially for reproduction of the plant.

EVIDENCES REGARDING FLOWER AS A MODIFIED SHOOT:

Generally, a shoot is characterized by the presence of nodes, internodes, leaves and buds. The axial stem bearing a flower is a thalamus.

It is very much condensed without showing distinct nodes and internodes. However, it bears floral leaves like calyx, corolla, androecium and gynoecium.

The internodes of the thalamus are very small so that all the floral leaves appear to arise from a single point. Following are some of the evidences to justify that flower is a modified shoot:

(i) Homology of the floral bud:

Both the floral and vegetative buds are similar in origin although the different in their outward appearance. It can be proved from the two aspects, viz., position and the fact that modification of floral buds, at times, into vegetative b bulbils.

(ii) Axis nature of the thalamus:

The thalamus on which different parts of a flower is placed is an axis W evident from the following facts:

(a) Development of internodes of the thalamus is marked in Cleome, Cap Pass flora, etc. In these cases thalamus is elongated and found with well develop nodes and internodes.

(b) As the calyx, corolla, androecium and gynoecium are placed on the thalamus sequence, it is evident that thalamus growth is limited by the carpel. In s cases, however, the thalamus grows beyond the gynoecium and bears a 1 shoot. It is known as monstrous development of thalamus a seen in rose.

(c) In Michelia champaca, the region of thalamus bearing carpels elongates like ordinary stem giving rise to an aggregate fruit.

(iii) Leaf nature of floral members:

The leaf like nature of the floral members such as calyx, corolla, stamens and carpel is evident from the following facts. Floral parts are modified foliage leaves and the characters that are marked in foliage leaves are also found in the floral members.

(a) The phyllotaxy or arrangement of floral leaves, i.e., sepals, petals, etc., on the thalamus (cyclic or spiral) – strongly resembles that of foliage leaves on stem.

(b) The floral leaves also show percolation as noticed in the foliage leaves. It is the arrange­ment of floral leaves with respect to each other (aestivation).

(c) In Mussaenda, one of the sepals becomes large and looks like an ordinary leaf. It shows the foliar nature of sepal.

(d) The transition of one type of floral leaves to another is also seen. In Nymphaea (water-lily), all forms of gradual transition, such as sepals to petals and petals to stamens, are found. In this case, there are a large number of floral leaves arranged spirally on the thalamus.

The sepals gradually merge into petals and petals gradually merge into stamens developing anthers on the top.

Presence of many petals in cultivated rose are really stamens, those have transformed into petals. In Hibiscus there are ‘single’ and ‘double’ varieties of flowers, it is thought that doubling is the transformation of some stamens into petals. In Canna, the stamens and the style have become petaloid.