On May 23rd, after finishing up a good book the day before, Darwin was back out collecting specimens around Botafogo Bay. Only problem was, he kept getting distracted by all the delicious tropical fruit:
“Collected numerous animals on the sandy plain, which skirts the sea at the back of the Sugar loaf. — The ground here being cleared of Cactuses & bushes is for many acres planted with Pineapples. They are cultivated in straight rows, & at a considerable distance apart. — Thus does this fruit nursed with so much care in England here occupy land, which for all other purposes is entirely sterile & unproductive. — The number of oranges which the trees in the orchards here bear, is quite astonishing. I saw one today where I am sure there were lying on the ground sufficient to load several carts, besides which the boughs were almost cracking with the burthen of the remaining fruit.” (May 23)
Darwin does like his tropical fruit – only a few days ago he was also talking about oranges, bananas and coconuts. And who can blame him – not only was it different from the apples and blackberries of home, it was typically a rare treat. As I mentioned in an earlier post (see Of Tamarinds and Baobabs) the long shipping times and lack of refrigeration made these fruits a true delicacy back in England. And it was one of the very first things Darwin got excited about when he arrived in Cape Verde. It is fun to see that he has not lost his appreciation for tropical fruit in the past four months!
Pineapple fields in Ghana (Wikipedia Commons):
So a few words about pineapples today…
Pineapples (Ananas comosus) belong to the Bromeliad Family (Bromeliaceae), which in turn, is part of the same order of plants as the grasses (Poales). Two of the most well know features of Bromeliads (though they are not true of all bromeliads) are that (1) many are epiphytes and (2) in some of the later their leaves are arranged in such a way that they can catch and hold water.
Epiphytes (or “air plants”) live in the tops of trees – thought they are not parasites and typically do not harm the tree in any way. (In fact, studies that look at what happens when you take epiphytes away from the forest canopy suggest that these plants may actually be beneficial to the tree.) Epiphytes simply use the tree branches a “shelf” which allows them to have more access to the sun. They get the nutrients and water they need out of the air. (Parasites on the other hand might “feed” off the tree itself.)
Tank bromeliads have an adaptation that makes it even easier for them to get the water and nutrients they need. The leaves are tightly packed together in a whirl that forms a “tank” for collecting water. This results in the formation of little “ponds” suspended in the tops of the trees. These ponds of water form oasis for other creatures who use them for a source of water or, in some cases, even live in them. (I continue to digress, but my favorite story is that of the tree frogs that raise their young in these tank bromeliad ponds to keep them safe from predators.)
OK, that being said, pineapples (the most famous and commercially successful bromeliad) is a terrestrial bromeliad. It grows on the ground and draws it nutrients and water from the soil (like more familiar plants do). Granted, not as exciting as the epiphytes, but much more tasty.
Pineapple (Wikipedia Commons)
The pineapple itself (named for its resemblance to a pine cone), starts as a cluster of flowers (called an inflorescence). The ovary of each flower develops into a fruit (basically a berry) and this cluster of berries is what grows together to form the pineapple that we eat.
Pineapple flowers (Wikipedia Commons)
Pineapples are actually believed to have evolved in southern Brazil / northern Paraguay, so Darwin was close to their origin here in Rio. Not long after European explores “discovered” them in the New World, the were carried back to Europe and cultivated in greenhouses as a special treat. Today, however, (according to the FAO) the pineapple market is dominated by pineapples grown in southeast Asia and Costa Rica.
Charles II receiving the first pineapple grown in England in 1675 (Hendrick Danckerts (via Wikipedia Commons):
So what is the connection between pineapples and math (or maths for those of you in the UK)? Well, the scales of a pineapple are arranged in spirals (see the diagram below from The Age Education Resource). The story goes that if you count the number of spirals in different directions, they form 3 consecutive Fibonacci numbers (say 5,8,13 or 8,13,21). The reality is that this is really only true for “perfect pineapples” – those with irregular shaped scales can vary quite a bit. But in an ideal world, it makes for a nice pattern – and who doesn’t like the beauty of mathematical patterns in nature! (RJV)
PS – For those not in the know – the Fibonacci sequence is the pattern of numbers you get when you start with 0 and 1 and add the two previous numbers together to get the next number in the sequence. So 0,1,1,2,3,5,8,13,21,34,55,89… It shows up a lot in nature.