Structure, Fertilization and Reproduction of Orchids

The chief characteristic of an orchid flower is the column, composed of the united male and female generative organs, stamens and pistil, and bearing upon it a small button-like projection known as the rostellum, covered, like the stigma, with a sticky glue like substance attractive to insects.

Orchids are fertilised by pollen-grains falling from the anther on to the stigma, or being deposited upon it by pollen bearing insects visiting the flower. Should the rostellum be touched by an insect (or even for purposes of experiment with a pin) the pollen masses are released from the anther at the top of the column. The column often bears wing-like, semi-transparent appendages that assist in the direction of insects to the rostellum.

At the base of the column is the ovary or seed capsule. The perianth consists of three sepals, forming the outer row, and three petals alternate with them, forming the inner row, all adherent to the ovary. The sepals are usually darker outside than the petals. A distinctive feature of an orchid flower is that the third petal or labellum (commonly called the lip) is usually unlike the others, and of strange and unexpected shape. In many cases the lip has a part to play in assisting fertilisation by insects. Its appearance attracts them. The rows of calli or glandular hairs upon it in some species, guide crawling insects to the base of the column. When the lip is fringed, insects often get entangled, and their struggles for freedom generally result in pollen being deposited upon the stigma. In some instances the lip springs forward at the lightest touch, being provided with a hinge-like contrivance, so that insects alighting on the lip are forced against the column and held there.

Some orchids, owing to the arrangement of the generative parts, are capable of self-pollination, but, the majority are dependent upon insects for fertilisation, the pollen usually being carried from other flowers. Those species that are selffertilised always produce a far greater proportion of seed.

The seed-capsule of an orchid is three-celled, each cell containing a great number of tiny seeds. The quantity produced is counterbalanced by the fact that the seeds do not germinate freely, and the enormous number of flowers on varieties dependent on insects for reproduction, that bloom and wither without being fertilised.

Although orchids seed freely when fertilised, the reproduction of terrestrial species is largely carried on by multiplication of the root tubers, and for this reason an orchid plant should never be torn heedlessly from the ground. If the flower is carefully picked from above, or even just below the lower leaf or leaves, no damage is done and it will grow up again.

West Australian Orchids Series

1. West Australian Orchids
2. Orchid Illustration 1 - Caladenia
3. Orchid Illustration 2
4. Orchid Illustration 3
5. West Australian Orchid Types
6. Naming and Classification of Orchids
7. Structure, Fertilization and Reproduction of Orchids (This post)
8. Collection of Orchids
9. Glossary of Orchid Terms
10. Caladenia
11. Diuris
12. Drakea
13. Eriochilus
14. Glossodia
15. Leptoceras
16. Lyperanthus
17. Microtis
18. Prasophyllum
19. Pterostylis
20. Thelymitra

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Related posts:

1. Collection of Orchids
2. Naming and Classification of Orchids
3. West Australian Orchids
4. Glossary of Orchid Terms
5. Glossodia

Tags: orchid fertilization, orchid reproduction, orchid structure