The botanical name of tomato is Solanum lycopersicum.

The tomato is native to western South America and Central America. Native versions were small, like cherry tomatoes, and most likely yellow rather than red. People have long used tomatoes in their cooking and the exact date of domestication is unknown. By 500 BCE, it was already being cultivated in southern Mexico and other areas. The Spanish explorers transferred the small yellow tomato to Europe around 1500 CE and later to Southeast Asia.

Although tomatoes originated in the Americas, they have become extensively used in Mediterranean cuisine.

The tomato is now grown worldwide for its edible fruits. Cultivated tomatoes vary in size, shape, taste and appearance, The most widely grown commercial tomatoes tend to be 5–6 cm in diameter. Most tomatoes are reddish orange but some can be yellow, orange, pink, purple, green, black, or white.

About 161.8 million tonnes of tomatoes were produced in the world in 2012. China, the largest producer producing 50 million tonnes in 2012.

Botanically, a tomato is a fruit: the ovary, together with its seeds. However, the tomato has a much lower sugar content than other edible fruits, and is therefore not as sweet. Typically served as part of a salad or main course of a meal, rather than at dessert, it may be considered as a vegetable.

 

 

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A tomato flower contains a green calyx which is made up of 5 separated sepals. The corolla is made up of 5 separated petals. The anthers are yellow in colour and they are fused together.

 

A flower is a reproductive structure of a plant. Many flowers have both male and female reproductive organs, though some are of a single sex. The floral parts are borne in whorls. The outer whorl is called the calyx, the next, the corolla. Within the corolla is the androecium and finally the gynaecium.

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The 4 whorls of the flower separated from one another

 

The calyx consists of sepals, which is usually green and small. They enclose and protect the rest of the flower while it is in the flower bud.

The corolla consists of petals, which are often coloured and scented. They attract insects which visit the flowers and collect nectar and pollen, pollinating the flowers as they do so.

The androecium is the male part of the flower and consists of stamens. The stalk of the stamen is the filament. At the end of the filament is the anther which produces the pollen grains. The pollen grains contain the male reproductive cells or gametes.

The gynaecium is the female part of the flower. It consists of carpels, which may be single, many and separate from each other, or joined together. In the carpels there are ovules. The ovules contain the female cells or gametes (ie the eggs). Ovules are enclosed in a case, the ovary. Extending from the ovary is the style, expanded or divided at one end into a stigma, where pollen from another flower or the same flower will be received. The ovules when fertilized will become seeds, while the whole ovary will be the fruit. The wall of the ovary develops into the pericarp (fruit wall) of the fruit.

The half-flower

A drawing of a half-flower is a convenient method of representing a flower structure. The flower is cut in halves with a razor blade, the outline of the cut surface drawn, and the structures visible behind these filled in.

 

drawing
From Mackean, D.G (1962) Introduction to Biology, John Murray

 

The anthers of the 5 stamens fused together to form a syngenesious stamens.
The anthers of the 5 stamens fused together to form a syngenesious stamens.

In this domestic variety of tomato, the anther is shaped like a hollow tube, with the pollen produced within the structure, rather than on the surface. The pistil lies within the anther, which facilitates self-pollination. In the wild type, the pistil protrudes out of the syngenesious stamen promoting cross-pollination.

The stigma and part of the style under the microscope
The stigma and part of the style under the microscope
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When the mature syngenesious stamens are cut opened by a razor blade, the stigma and the style are visible. The stigma is covered with pollen grains.

 

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The ovary has been cut open transversely. 2 carpels with many ovules can be seen. The diameter of the ovary is about 1 mm. The structure has been magnified under the microscope.
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Similar ovary is cut open longitudinally, 2 carpels with many ovules can be seen under the microscope.

 

Pollination is the transfer of the pollen grains from the anthers to the stigma of the same flower or a different flower of the same species.

After pollination, fertilization takes place. Fertilization is the fusion of the male cell and the female cell to form a zygote. Then the zygote divides many many times by mitosis to form a baby plant. The process has been oversimplified here.

The ovules become seeds and the ovary becomes a fruit .

 

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After pollination and fertilization, the petals withered and dropped off. The stamen dried up and will fall off soon.

 

From Mackean, D.G (1978) Introduction to Biology, John Murray
From Mackean, D.G (1962) Introduction to Biology, John Murray

 

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The ovary has grown fast and enlarged many many times.
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The sequential development of a flower into a small fruit
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The calyx still remains on the ripe fruit

 

 

drawing (4)
From Mackean, D.G (1962) Introduction to Biology, John Murray

 

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The sequential development of the ovary (about 1 mm in diameter) to a ripe fruit (about 63 mm in diameter). Only the transverse sections are shown.

Using the formula  V = ⁴⁄₃πr³  (V = volume, r = radius)

The volume of an ovary is about 0.5 mm3, the volume of a ripe fruit is about 130 000 mm3,

The ovary has enlarged about 250 000 times.

Tomatoes have the chlorophyll pigment when they are raw and hence they are green in colour. As they start ripening, the pigment lycopene becomes dominant and this is why tomatoes turn red.

Lycopene is a carotenoid and belongs to the same family as beta-carotene. It is a powerful antioxidant that neutralizes free radicals.

 

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Flowers are borne in a cyme of three to 12 together
The calyx still remains on each tomato fruit and the fruits are joined together.
The fruits are joined together like the cyme of flowers.  The calyx still remains on the fruit.

 

 

Acknowledgments :

I would like to thank the late Mr Donald C Y Siao and Fr A Bogadek, my Biology teachers in Hong Kong for teaching me the fascinating structures of the flowers. I would also like to thank Joe for the tomato specimens.

 

Bibliography :

Mackean, D.G (1962) Introduction to Biology John Murray

Mackean, D.G (1978) Introduction to Biology (Colour Edition) John Murray (0 7195 3676 6)

https://en.wikipedia.org/wiki/Tomato

 

 

 

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