Why Is A Banana Curved? | Windowthroughtime

For such a commonplace ingredient in our diets, there are plenty of misconceptions about bananas, not least that they grow on trees. Botanically, a distant relative of ginger, the banana fruit is a berry grown on an herb bush, albeit the world’s largest flowering herbaceous plant. All the visible parts of a banana plant come from a corm.

What looks like a trunk is really a pseudostem or “false stem”, produced when the base of the stalk of its leaves or petiole widens to form a sheath. The edges of the sheath meet when it is first produced but the pressure of new growth within the pseudostem pushes them apart. Even though the plants can reach well above five metres in height, this is all that supports them and their bunches of bananas.

When the plant reaches maturity, it stops growing new leaves and develops a banana heart or inflorescence inside the pseudostem, which pushes its way to the top. Once there, it produces rows of banana buds, looking like big red cones, running down a long, knobbly stalk. The buds positioned further up the stalk and closer to the leaves become female flowers which are the ones that produce the fruit. The male flowers on the lower end of the stalk are not needed for pollination and quickly drop off the plant.

The developing fruits start to grow downwards and begin to take the form of slender bananas, green in colour and looking rather like rectangular fingers jutting out in rows from the stalk. As they increase in length and weight, they begin to sink ever more alarmingly towards the ground, the natural consequence of gravity. It is at this point that negative geotropism steps in.

Geotropism is the term used to describe how the parts of plants grow in response to the force of gravity. The natural reaction of most plants’ roots is to grow downwards in line with the force of gravity, an example of positive geotropism. The banana, too, initially grows downwards but the urge to find sunlight, prompted by a plant hormone called auxin, causes it to defy the pull of gravity. In a classic exhibition of negative geotropism, it effectively folds in against itself to create the distinctive curved shape we associate with the fruit.

Why it does this is down to its original natural habitat. Banana plants grew in the middle layer of rainforests, where sunlight is hard to find. Most plants in search of sunlight would grow sideways but the structure of the banana plant, lacking a solid trunk and now laden with fruits that are growing increasingly heavier, means that it would become unstable and eventually topple over.

Typically, the hanging clusters of bananas will be made up of between three and twenty tiers, with each tier containing up to twenty fruits. These bunches or “banana stems” can weigh between thirty and fifty kilograms, with each individual banana tipping the scales at around 125 grams. Its only option in order to bear the weight and maintain stability is to force its fruit to bend and curve upwards. After fruiting, the pseudostem dies but the plant is classed as a perennial because an offshoot will have established itself at the base.

Modern cultivars, there are now over 1,000 different varieties, subdivided into fifty groups, have been selectively bred to accentuate the graceful curve, which, with its colouring, has become its distinctive feature. However, straight bananas do exist, especially in the wild. Perhaps the best-known is the Lady Finger, also known as a sugar banana, which is around five inches in length, thin skinned, and sweet.

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