Inflorescence, Flower, Fruit and Seed: Quick Revision

A brief note on Inflorescence, Flower, Fruit and Seed. Read it before a test. Try each question at the end before you open its answer.

The inflorescence

• Racemose: the main axis continues to grow. Flowers open in acropetal order: oldest at the base, youngest at the tip.
• Cymose: the main axis ends in a flower. Growth is limited. Flowers open in basipetal order.
• The pedicel carries one flower. The peduncle carries the cluster.

The flower

• Four whorls: calyx (sepals), corolla (petals), androecium (stamens), gynoecium (carpels).
• Symmetry: actinomorphic (radial), zygomorphic (bilateral), asymmetric.
• Ovary: hypogynous is superior; perigynous is half inferior; epigynous is inferior.
• Aestivation: valvate, twisted, imbricate, vexillary (pea).
• Stamens: an anther has four pollen sacs. Epipetalous, epiphyllous; mono-, di- or polyadelphous.
• Carpels: ovary, style, stigma. Apocarpous (free) or syncarpous (fused).
• Placentation: marginal, axile, parietal, free central, basal.

The fruit and the seed

• A fruit is a mature ovary. A parthenocarpic fruit forms without fertilisation (banana).
• The pericarp has an epicarp, a mesocarp and an endocarp. Mango and coconut are drupes.
• A dicot seed (gram, pea, bean) has a testa, a tegmen, a hilum, a micropyle and two cotyledons. Most are non-albuminous; castor is albuminous.
• A maize grain has a membranous coat fused with the fruit wall. It has a bulky endosperm and an aleurone layer.
• Its embryo has one cotyledon, the scutellum. A coleoptile covers the plumule and a coleorhiza covers the radicle.

A worked example

A mustard flower has $4$ sepals, $4$ petals, $6$ stamens and $2$ carpels. How many floral parts and how many pollen sacs does it have?

1. Floral parts. $4 + 4 + 6 + 2 = 16$ parts.
2. Pollen sacs. Each of the $6$ stamens has an anther with $4$ sacs: $6 \times 4 = 24$ sacs.
3. Ovary. The carpels are fused in mustard, so the flower is syncarpous, and it is hypogynous.

Practice with new numbers

A program to try

The program counts the parts and the pollen sacs of a flower.

Mistakes to avoid

• A racemose axis keeps growing; a cymose axis ends in a flower.
• Hypogynous is superior; epigynous is inferior.
• An anther has four pollen sacs, not two.
• Epipetalous is on the petals; epiphyllous is on the perianth.
• Gram, pea and bean seeds lose their endosperm; maize keeps it.

Check yourself

1. In which order do the flowers of a raceme open?

2. Name the position of the ovary in guava.

3. How many pollen sacs are there in 5 stamens?

4. Name the three layers of the pericarp.

5. Which part of the maize grain is the single cotyledon?