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Foxgloves (Digitalis purpurea)

The foxglove is a marvellous example of a plant which is adapted to be pollinated by insects.  It clearly shows how certain parts of the plants have been specially modified over time so that it is able to attract insects. Such modifications are called adaptations. It needs to attract insects so that its flowers can be pollinated. It is only after the flower has been pollinated that fertilisation can take place and the flower can produce seeds.  The main adaptations are as follows:- 

  • The foxglove is tall (1.5m) so that it can be seen. Often a mass of plants grow in the same area maximising the visual signal to passing Bumble bees.
    Bumble bees, of which there are many species, are the main pollinators of foxgloves.

  • The foxglove is purple. Bumble bees are particularly attracted to this colour.  Interestingly their eyes are not sensitive to all the colours of the spectrum. They are colour blind to red although they are sensitive to blue, green, orange, yellow and ultra violet.

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  • Often the weather during the summer may be cold and wet for several weeks at a time. As a result insect activity is minimised and the chances of pollination much reduced. To overcome this the Foxglove has an extended flowering period. It starts flowering in late May or early June and continues through to September. The flowers are first produced on the bottom of the flowering stalk or raceme. In turn, each of the flowers matures in succession. The last to mature is therefore the flowers on the very top, the highest point. Thus the flowers are still visible even if the surrounding vegetation has grown up. Note the green immature flowers at the tip and those which are mature and therefore open.  Also that those flowers which are in an intermediate stage are purple and hence attract insects. However the mouth of the flower is kept closed until the flower is ready for pollination.
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  • A bee's eye view of the open foxglove flowers. Note the wide open mouth of the flower. It has a lip or landing place which sticks out of the entrance. The entrance also has guard hairs which deter smaller insects from crawling into the flower. The hairs may also offer some support to the bumble bee as it often scrambles for grip upon landing. The downward shape of the flower also acts as a deterrent to smaller invertebrates.

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