The world below

Journey to the Centre of the Earth is a famous science fiction novel written by the great Jules Verne in 1864, as well as a series of films based on it, the first of them in 1959, with the same title. It tells of an underground world, in the depths of the Planet, where monstrous creatures, giant mushrooms and dinosaurs live. There is no sunlight down there, beneath the volcanoes and ocean floor, and yet, in the film there are pterodactyls gliding across a sky lit by the radioactive rocks of a cave so large that it contains an ocean. The novel is clearly the brainchild of the man who practically invented science fiction… But is it all really impossible?

The answer is no, and recent discoveries have revealed an underground world full of life forms that have never seen the sun. These are bacteria that teem miles below the Earth’s surface, far below the deepest of oceans. It is a dark and icy world which, according to Canadian researchers who are exploring it, is nevertheless immense, ancient and extremely rich in biodiversity.

But how do those bacterial cells survive in such extreme conditions with no sunlight and a perpetual shortage of organic matter to eat? The answer is simple and incredible: they live off radioactivity. Was Verne right? In a way, yes: deep underground there is a living community that thrives on nuclear processes involving the radioactive atoms in the rocks. Radiation does in the underground what the sun does on the surface by means of photosynthesis, that is it breaks the water molecule into its atomic components: hydrogen and oxygen, by a process called radiolysis. The phenomenon of water radiolysis was observed for the first time by Marie Curie at the beginning of the 20th century when she noticed how bubbles of hydrogen and oxygen developed from a solution of water and radioactive elements. Bacteria living in the depths are able to obtain energy from hydrogen. This is a mechanism that evidently works very well, in fact these simple and tenacious life forms have been found in rock samples taken from the beds of seas all over the world.

Research groups exploring deep life also include planetologists and astrobiologists, namely scientists who study what life on other planets might look like. The subsoil, in fact, is a natural laboratory for understanding how life could have developed on distant worlds, in conditions very different from those that we, surface earthlings, know very well.

By Andrea Bellati

Going further back in history to the time of the Aztechs, we find another legend, according to which the plant is said to originate from a drop of blood from the broken heart of a goddess in love. The Aztechs called this plant “Cuetlaxochitl”, meaning “Flower that withers, mortal flower that perishes like all that is pure”. The Cuetlaxochitl was grown as a gift from the gods and Montezuma, the last king of the Aztechs, used it to decorate his palaces. The Aztechs also used the milky sap of the Cuetlaxochitl to cure fever and a red pigment used to dye fabrics was extracted from its bracts.
In 1804, the plant was brought to Europe for the first time by the naturalist scientist Alexander von Humboldt. It was catalogued in Berlin and given the botanical name Euphorbia pulcherrima: the most beautiful of the euphorbia. Around 1828, the American ambassador to Mexico, Joel Roberts Poinsett, an amateur botanist, took the plant to South Carolina, in the United States. And it was precisely there, in honour of Poinsett, that it began to be called “Poinsettia”. Moreover, since 12 December 1852 – the anniversary of Poinsett’s death – in the United States “Poinsettia Day” is celebrated. It has become a tradition to exchange Poinsettias on this day – a nice custom that is beginning to catch on in Europe too.

From South Carolina, the plant spread to various parts of the United States where the climate was sufficiently warm, including California. Fascinated by the beauty of the red plants that grew wild close to his ranch in California, a plant grower called Paul Ecke decided to start cultivating them. He then began selling the cut branches at Christmas, expanding sales to the whole of the United States. It was apparently the Ecke family’s marketing that promoted and spread the association between Poinsettias and Christmas all over the world.

In its wild state, the Poinsettia is a bush that flourishes in the sub-tropical climate of Mexico and grows to as  much as 4 metres in height. Its greatest beauty is without a doubt its “blooms” but, contrary to what is generally thought, its flowers, known as cyathia, are not red but yellow and are surrounded by a crown of red bracts. In botany, bracts are modified leaves that accompany flowers or inflorescences.  The actual leaves are green but during the winter period they are almost entirely hidden by their red “sister” leaves.

It is a typically photoperiodic or short-day plant; this is why it flowers in the middle of winter when the days are shortest. A good amount of light favours luxuriant growth, but in order to foster blooms, the plant must stay in the dark for a large part of the day.
At our latitudes, it needs to be grown in greenhouses, where over 100 varieties are cultivated. In fact, since it is easy to hybridize, it is offered in new versions: besides the conventional red ones, the most popular, the colour of the bracts may also be cream, powder pink, variegated and edged in white, orange or yellow.  Their shape may also vary: lanceolate, dentate or even “curly”… Blue poinsettias, produced by artificial colouring, are less long-lasting.

It is not always easy to keep Poinsettias healthy in our homes. However, it is not impossible: here are a few simple hints on how to make these plants last even beyond the Christmas period.

Poinsettias survive well in brightly lit rooms with temperatures between 15 and 22°C, but they do not like cold temperatures, sudden changes in temperature and draughts.
The ideal temperature, to ensure that they have the deep colour that we know, is around 18°C and, if nebulised regularly with water, they will bloom longer.
They suffer when exposed to direct sunlight and if too much water is allowed to remain in dishes beneath pots. Moreover, they suffer when watered directly on their leaves.
Use of fertilisers is not recommended when they are flowering; after blooming, they should be fertilised once a month.
Contrary to what we are used to thinking, Poinsettias do not die just a few weeks after purchase. Plants should not therefore be thrown away when the flowers fade and the plants lose their leaves and bracts, but should be pruned leaving stems no more than 10 centimetres long, repotted and placed outside, in a place that is well-lit but not exposed to direct sunlight. In October and November they must be kept in the dark (or covered with a black bag) for at least 15 hours a day, from the afternoon to the following morning. It is precisely the dark, in fact, that favours the vegetative stage and development of red bracts.

by Benedetta Palazzo