The plant pollination process describes the vital method of sexual
reproduction in plants. It enables a plant to bear fruit and seeds,
many of which are not only eaten by humans, but also by other living
species from birds to mammals. Birds and mammals may then distribute
those seeds to new geographical locations through their droppings.
The pollination process involves the transfer of pollen, from the male part of a plant (in flowers, this is the ‘stamen’) to the female part of the plant (the 'carpel'). The pollen contains male sperm (gametes), and the carpel is where the female gametes are contained.
This photograph of a lily clearly shows:
- the male part of the flower: comprising the anther and filament (together, called the ‘stamen’); and
- the female part of the flower: the stigma and style with the ovary (containing the ovule) at the base of the flower (the ‘carpel').
The following points correspond to the diagram opposite.
1. Pollen grains land on the sticky stigma.
2. A pollen tube grows down the style, followed by male sperm nuclei.
3. The sperm nuclei fuse with the female ovules.
4. The ovules develop into seed, and the ovary develops into fruit.
In most cases, more than one individual plant is needed.
This means that pollen is transferred from one plant, to another individual plant.
This, in a nutshell is ‘cross pollination’.
However, some plants have evolved the ability to self pollinate. ‘Self pollination’ means that an individual flower on a plant stem can pollinate itself, or other flowers on the same individual plant stem.
Where plants need other plants, how does this transference of pollen occur?
About 80% of plant pollination requires the help of other living, moving creatures such as insects, birds, or bats, to transfer pollen from one plant to another.
This is called ‘Biotic Pollination’.
Where this is the case, plants are adapted to encourage the specific pollinators they need - they are said to have developed 'pollination syndromes'.
Very often, the pollinating creature will receive some form of reward – this is the creature’s incentive to visit the plant - perhaps a portion of the nectar or pollen produced by that plant specimen. Of course, insects such as bees require nectar and pollen for food - you can read more about this on the page: Why Do Bees Need Nectar And Pollen? (Bees have also evolved different methods of gathering and carrying pollen - read about it here).
However, this is not always the case - the insects do not always get the desired reward! Some plants it seems, have devised cunning ways to cheat the very creature it needs for the pollination process to occur – in other words, the creature (usually an insect) enters a flower, pollinates it upon doing so, only to discover there is no reward at the end of their endeavours!
However, it works both ways.
Some insects, for instance, have devised ways of robbing nectar without pollinating the plant at all.
You can read more about this on my page describing flower pollination.
What about the other 20% of plants, how are they pollinated?
Well some plants, especially grasses, most conifers, and some deciduous trees, are pollinated by wind.
This is called ‘anemophily’.
The structure of the plant is adapted to enable pollen grains to be blown from one plant onto another.
However, a small number of plants – water plants - rely on water movement for pollination.
This is called ‘Hydrophily’.
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