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Lily flower bud

Spike Walker

Download this image from Wellcome Collection.

Light micrograph of a stained slice of a lily flower bud showing the male and female reproductive organs. At the centre of the image is the pistil, the female part of the flower, which contains six egg cells (ovules) housed in an ovary. This is surrounded by six male anthers (the white material) each containing four pollen sacs (the red circles), which are filled with pollen grains. Pollen grains contain the male sperm cells. After an egg cell is fertilised by a sperm cell it develops into a seed. Around the outside of the bud are three petals (small, circular in shape) and three sepals (large, triangular in shape). The width of the image is 10 mm.

How was this image created?

The lilium bud was stained (most likely with safranin) and then viewed with a light microscope using dark ground microscopy. In dark ground microscopy the sample being imaged is lit from the side using scattered or peripheral light rays (direct light is blocked out), and it is these that are captured by the objective lens. The resulting image is a brightly lit sample on a dark background. If there is no sample on the microscope stage then the entire field of view will be dark (hence the name dark ground or dark field microscopy). This technique can be especially useful when trying to separate an object from its background, for example if the two are similar in colour. The technique is similar to backlighting an object to give it more contrast.

What is the difference between a petal and a sepal?

Sepals are modified leaves that enclose the flower bud to protect it as it develops. They are often green in colour, but can also be colourful like petals. Petals are often brightly coloured to attract small insects such as butterflies and bees to the flower to encourage pollination. Some flowers, like lilies, have very similar looking sepals and petals and these are collectively called tepals. Lilies belong to the group monocotyledons, one of the two main groups of flowering plants. One characteristic of monocotyledons is that their flower parts are usually arranged in threes.