9 de noviembre de 2015

Mandarin Microsegments

The other day, I was eating a mandarin (it's like an orange, but sweeter and very easy to peel). I pulled the bottom half of the shell in one piece. In the center (exactly on the opposite point of the stalk) it had a lot of microsegments, about 10 or 15 of them. I really don't know the name of these things, but they are like very small segments of 1mm or 2mm (1/16'').

[I'm not sure if the correct translation is "mandarin", or tangerine or clementine or any of the other variations I found. Here in Argentina we call all of them "mandarinas", and I ate it before having time to classify it.]

Bottom half of a mandarin shell.
In the center there is a bunch of microsegments.

Zoom of the microsegments in the mandarin.

I had never noticed this before. I guess it would be better to eat a few more mandarins and see if it is normal or if it was only an exception, but it's more fun to invent theories (and I couldn't find any explanation in internet).

I was always surprised that the number of segments in oranges and mandarins varies randomly. I guess between 8 and 12 because if you split one of them into 4 parts (following the usual direction), there are generally about 2 or 3 segments in each part. I never did a statistic. (Is it like a Gaussian? Poisson? It depends on the variety? Is it correlated with the weight?)

[In mandarins, I think that each segment has one or two seeds. (In oranges it is more difficult to count because they are more difficult to peel, and you have to cut it, so the segments get broken.) One possibility that I thought is that when the fruit is formed, there are initially a lot of small segments, and those which have seeds grow and the others remain small. Sounds good. If I remember correctly the growth of the strawberries is related to the seeds, but I'm not a biologist ...]

For comparison, a well known example are apples. When cutting an apple in half by the "equator" you get always the same figure. (That is, cutting it in the direction perpendicular to the usual cut, so the stalk in one half and the thing at the bottom in the other half.) (Worth trying yourself. It's a nice experiment. Find an apple and try before continuing.)

Apple cut in half by the "equator".
It has a 5 pointed star shape.

The surface of the cut apple has a symmetrical shape that has 5 parts and looks like a star (D5 for the perfectionists). Actually, the thing at the bottom also looks like a 5 pointed star if you look at it optimistically. Many flowers (including apple flowers) have 5 petals, so I guess some internal structure is repeated 5 times and I guess that is related to the 5 parts of the apple, but I'm not a biologist ...

Another example are bananas. If you cut the banana in slices, you get a quite symmetrical shape with 3 parts (D3 for the perfectionists). Also, if you press slightly a peeled banana on the sides, it gets separated in 3 parts. (In general, the banana gets slightly crushes in this experiment, so you must be careful to separate the parts and anyway you'll get a small mess ...) (I can't image an excuse to explain the 3. Are they actually 5 parts but 2 of them are very small?)
Two slices of banana.
It has a shape with 3 parts.

To think about:

(Not much to think about, but it's an easy subject for experiments.)
  • Eat a few mandarins, and see if the the microsegment are normal. Do you always get them? Do they get glued to the other segments instead of being glued to the shell? Repeat the experiment with other citrus fruits. (For example, some seedless oranges have a strange thing in this site, like a circle of 1cm (1/2'') little segments ...)
  • Go to the grocery and get other fruits (and vegetables) to split them by the "equator" and see what shape you get. Is it symmetric or almost symmetric? Is it like a deformed symmetrical figure? How many parts do you get?