The colour of the flowers is the variable in the above-mentioned experiment.
It is a method of performing cross-pollination where the transfer of the pollen grains from the anther of one flower of a plant to the stigma of another flower of a plant happens by the insects.
It is often called insect pollination. The flowers that are pollinated by insects have attractive petals of bright colours. This adaptation ensures that the insects will be attracted to the flowers.
The nectar present in these flowers, on which the insects feed is also sweet with an attractive scent. This is another factor which attracts the insects to the flowers.
It is by way of sucking the nectar that the insects also get pollen stuck on their mouth regions and legs. The pollen grains produced by these flowers are also sticky.
Therefore, to examine if monarch butterflies prefer a specific coloured flower, different plants with different coloured flowers need to be used and the colour of the flowers will be the variable.
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