Why do oranges have peels?
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This is But Why, a podcast for curious kids from Vermont Public. I'm Jane Lindholm. On this show, we take questions from curious kids just like you, and we find answers. You all are so interested in so many things that we never know where your questions will take us. This time, your curiosity took us on a field trip to Florida so we could get an expert to help us with these kinds of questions.

Why do oranges have peels? Why fruits are so juicy. How do seedless oranges reproduce? I'm pretty curious about citrus fruits too, so I headed to the Southwest Florida Research and Education Center at the University of Florida to talk with a professor named Fernando Alvarez.

He's a citrus horticulturist, a plant guy who focuses on citrus fruits like oranges, lemons, limes and grapefruits. I work on citrus research, as I like to say, from seed to table. And that means that I have some projects working on citrus seeds. I have projects working on the small citrus trees, how they grow.

how they set fruit and then how we can improve the quality of that fruit. So when you eat that fruit, it's the best that you can eat.

Oranges, and orange juice in particular, is very important to the economy in Florida. And you might drink Florida orange juice with your breakfast in the morning. So having people like Professor Alferez who can study how to make these plants grow well and produce tasty fruit, but also how to protect them from disease and invasive species, is really important work.

Since Professor Alferes knows so much, we put all of your questions to him. But first, we wanted to get a real basic one out of the way. What is a citrus fruit? A citrus fruit is a fruit that is...

we call botanically an hesperidium. That's a pretty cool word. Citrus fruits are in a group called hesperidium, which is a type of modified berry. They're related to other berries like blueberries or raspberries, but they have a tough, leathery outer rind and an inside juicy or fleshy part that's divided into sections. Citrus fruits include oranges, mandarins, lemons, grapefruits, pomelos, and limes.

Generally speaking, a fruit of any kind has one specific job. What a fruit does is just to protect the seeds. That's right. The job of a fruit is to protect seeds. Fruit begins as a flower. Flowers will grow on a tree or bush, bloom, get pollinated, grow bigger, and then the petals wither away.

but the fruit has been fertilized and is still growing. The ovary, usually the middle part of a flower, starts to enlarge. Inner pieces of the ovary, called ovules, will develop into seeds. Around the seeds, the ovary expands into what we think of as the fruit. And, as we said, the purpose of a fruit is to protect those seeds. As you probably already know, seeds are needed for reproduction to make the next tree or bush.

Some fruit seeds make a new plant with fruit that tastes just like the parent plant it came from. But others, including apples and citrus fruits, don't. So if you spit out an orange seed and it manages to grow into a new tree, the oranges it produces won't necessarily be the exact same flavor.

But citrus farmers want to make sure that every navel orange or mandarin or key lime tastes the same because people who buy them get used to those certain flavors.

So rather than take a gamble and plant all of their trees from seeds, they usually take a branch from a tree they know the flavor of and attach it to the roots of a new young tree. The branch will fuse to that root stock, and the new branches will bear fruit that tastes just like the older tree they originally came from. That process is called grafting.

Here's a question from John. And I'm four years old and I live in Turkey, Istanbul, and my question is: Oranges shaped like a ball? That's a very interesting question and it looks simple but this is really profound and it has to do with shape in nature. Usually different shapes in nature

they have a role, they are not random and in the case of why they are like balls or like a sphere is because efficiency. Let's say that a sphere gives you the less area for a given volume, okay? And that means at the end means less exposure. So it's the way that the fruit

can protect better the seeds. So that's why most of the fruit, including oranges, are like balls. But lemons and limes aren't quite shaped like balls. They're shaped more like American footballs. Yeah, that's right. Well, there is some variation there.

A ball shape means there's less overall area on the outside of the fruit that can get punctured by an animal or exposed to challenging weather conditions. And inside the protection of the peel, that shape provides a lot of room for juice and pulp to protect the seeds. You know how when you peel open an orange it has sections, and then you can just pull those sections apart and eat them one by one without all the juice spilling out? Kevin has a question about that.

I come from Maui and I'm nine years old. And my question is, how are oranges pre-sliced? What role do the segments play and why have they developed? Yes. And actually you can see between, let's say in general, between 10 and 15 segments per fruit, depending on the variety. And every segment will have typically one or more seeds.

And why this is organized in that way? There is not a clear answer, but one theory that is easy to understand, it facilitates seed dispersal. So if you have your seeds divided in segments, probably it's easier for those seeds to be dispersed by different animals.

So all the seeds will be dispersed in different places. Okay, that's what I have read about it. Now, I would like to know if an animal is able to eat only one segment and leave the rest for other animals. I would not be able to do that.

No, I don't think humans are very good at that. We may be able to divide the segments, and if we have to, we'll share with a friend or a sibling. But yes, I don't think an animal biting into it is likely to leave some segments. But

If seed dispersal or the way the tree has developed to make sure its seeds get spread is by having animals eat those seeds, which a lot of plants use that as a method of seed dispersal, why do they have such a tough peel?

Humans don't usually eat the peels of oranges, although we can eat the peels of some citrus fruits, but we usually don't. They're kind of bitter and they're tough. So why have such a tough peel if the fruit is supposed to be eaten by an animal? My name is Jed from three years old, and I live from range. And why do apples have skin? You do eat apples.

And why do bananas and oranges skin on peels that you don't eat? My name is Sage. I am seven. And I live in Madison, Alabama. Why do oranges have peels? Hi, my name is Ava. I am four years old. I live in Illinois. Why are there peels on an orange? Yeah, well, that's again...

for protection. And that's for protection when the fruit is growing and the seeds are developing. At some point when the fruit gets into maturation, pills are not that tough. They are more soft and animals can actually access without any problem. And that comes at the end of the maturation

that the fruit can also drop from the tree and is accessible to animals. I didn't realize that, that the skin of citrus fruits becomes less tough as the fruit matures. So it's really good at protecting the fruit as it grows and ripens, and then once the fruit is ripe and it's time for an animal to eat it, or for the fruit to fall to the ground and go into the dirt, then the skin or peel becomes less tough.

My name is Ellis. I'm from Wisconsin and I'm four years old. And I want to know why fruits are so juicy. Fruit are cool.

Ellis and Felix both want to know about why fruits have juice, and citrus fruits are full of juice. It's to make them appealing to animals, and also consider the fruit as what we call a zinc organ in the plant. So it accumulates sugars, so it accumulates the juice, and because of the sugars, it makes it desirable for the animals as well.

So some of the sugar that the plant creates during photosynthesis gets stored in the juice vesicles within the fruit itself. And that's pretty appealing to animals who want to eat those fruits. And then the animals will poop out the seeds in various places, not just right where the original parent tree is. And that's one of the ways trees have evolved to get seeds to new spots. OK, but what about seedless fruit?

My name is Maisie. I'm from Valley Stream. I'm seven years old. How do seedless oranges reproduce? Hi, my name is Arlo and I'm eight years old and I live in Charlotte, North Carolina. How do they get the seeds out of seedless fruit like seedless watermelon and seedless clementine if they have to be planted from a seed?

One of the things you mentioned was that the whole point of a fruit is to protect the seed, to grow and protect a seed so that that seed can grow into a new tree.

But sometimes when we buy fruits in the grocery store, they are what are called seedless fruits. And so, because we don't really like to eat the seeds, they don't taste very good, they're hard to spit out. So a lot of fruits have developed that are seedless fruits you can buy. But how is that even possible if the whole point of the fruit is to protect the seed and when the tree is growing, the fruit is supposed to make seeds? How in the world do we get seedless fruits?

Yeah, that's a great question. Many of the efforts from researchers and the industry is to develop seedless fruit. You can do that by breeding, by hybridization, and in some cases even by irradiating the bad wood

for instance with gamma rays and you can get you can get a bad wood that doesn't produce seeds anymore. There are a lot of commercial varieties that don't produce seeds because we did that and that's a trend since many many years ago because for instance I can tell you the story of one of the most

salt grapefruit here in Florida. It's the Duncan grapefruit. At some point it was really, really popular in the state because the taste and the flavor, but it may have 70 seeds per fruit. So it was impossible. So what happened was that people all decided not to grow it again.

or to grow it anymore because that amount of seeds. So at some point it was not marketable anymore. So that's what happened. So the trend is to try to

to reduce the number of seeds. And you can do that by breeding, mostly. I don't think I would want to eat a fruit that had 70 seeds either. So farmers have found ways by selective breeding or by radiation to create trees that produce fruit with fewer seeds.

By breeding, that means you select varieties that have fewer seeds and pick those plants to reproduce. And remember, most citrus trees are made by grafting, so you can use a branch from an original tree to create a new one without having to start with a seed at all.

I'm eight, I live in Williston, Vermont. Why do lemons have seeds but limes don't? Well, there are limes that have seeds and there are lemons that don't have seeds. So in some cases, as I just described, I mean, we always try to breed a fruit

seedless or almost seedless so because then it's easier to market

And in the case of lemons, if you are squeezing a lemon and you get all the seeds in your food, you don't like that. So we always try to get rid of the seeds. The limes that we most typically find in U.S. grocery stores are Persian limes. And these limes, a cross between a key lime and a lemon, don't naturally reproduce through seeds. So the farmers who grow them use that grafting technique we've talked about to make new lime trees, and the limes they produce don't have many seeds.

But other types of limes do have seeds. Coming up, why are those limes so sour? This is But Why, a podcast for curious kids. I'm Jane Lindholm. We're answering your questions about oranges, lemons, and limes with Professor Fernando Alferes at the University of Florida. My name is Kimiko, and I'm eight years old, and I'm from Austin, Texas. Why does lemon taste so sour?

Hi, my name is Hanley. I'm eight years old and I live in Arlington, Virginia and I want to know why are lemons sour? My name is Laura. I'm six years old. I live in Germany and what makes a fruit sour or sweet?

I'm Elijah. I'm six years old. I live in Great Neck, New York. Why are lemons sour? Lemons and limes are sour because they contain something called citric acid. That's an organic chemical that's in a lot of fruits. Citric acid is found in higher amounts in the more sour citrus like lemons and limes.

We have little taste buds, little body parts that can perceive taste on our tongue, the roof of our mouth, and the back of our throats. Those taste buds send information to nerves, which then send information about what we taste to our brain. And that's how we taste things as sour. Okay, now we have a question about juice from Dominic.

I'm eight years old. I live in Farmington Hills, Michigan. I wonder how many oranges it takes to make one gallon of orange juice. For a gallon of juice, okay, a gallon, if I am correct, is about 128 fluid ounces. And a regular orange has about six ounces. So if you do the

You do the math. You're getting out your calculator. Yeah. If you do the math, it's about 21 fruit per gallon of juice. That's a lot of oranges just to get our juice. But that's one of the most important agricultural products here in Florida, too, is that Florida exports a lot of juice to everybody else. Yes, and actually our production here in Florida is mostly orange.

is mostly focused on juice production. I would say that it's about 95% of the production here in the state goes to juice. My name is Alex. I am six years old, and I live in Palo Alto, California. And my question is, why are bananas and oranges here all year long and not pomegranates?

You go to the supermarket and you have citrus fruit all the time in the year. So what they do is to have different varieties at different times in the year. So you can see for instance a mandarin, let's say in as early as September, and you keep seeing that mandarin or you think it's the same mandarin because the brand is the same,

in October, November, December, January. But the variety is different and you don't notice. So they brand it the same way but they are different varieties. The same happens with oranges. You can have, for instance, and I'm working in Florida, so for instance you can have Hamlin oranges in the supermarket in October, November, December.

And then all of a sudden you will have Valencia oranges and those will come in January, February. So you have a lot of different varieties.

during the whole year. So you're telling me that oranges are seasonal too, but why do we have them in the grocery stores all year round and then we have certain fruits that only come at a certain time of year? Yes, that has to do with the number of varieties available. Pomegranates, probably they don't have that many varieties. But in the case of citrus, we

We estimate, and there is not a clear answer, there is nobody who knows exactly how many citrus fruits, different citrus fruits are there, but some estimate that it's more than 1,000, counting oranges, mandarins, lemons, limes, and other specialty fruits. So it's more than 1,000 probably. It's a huge amount. And in some places like Spain, for instance,

you can have 30 or 40 different varieties through the year. Now, if there are typically some months like June, July, August that you don't have fruit, what happens is that we import fruit from other areas. We are in the northern hemisphere, so we produce the fruit from September to, say, May, June. But then,

July, August, and even early September we will import fruit from the southern hemisphere. My name's Maddie and I'm seven. I'm from Nampa, Idaho. And my question is, why is the fruit orange and the color orange called the same thing? Why are oranges called oranges, at least in English? The word is really an ancient word.

And the origin is from a language that was spoken like 3,000 years ago in Northern India. That's the Sanskrit that gave origin to different languages, including English and Spanish and others. And it was called Naranga, which is N-A-R-A-N-G-A. And that means fragrant.

That means fragrant in Sanskrit. Fragrant, like smells good? Yes. The Spanish word is the same as naranja. You just change the "g" for a "j", okay? And if you consider the word orange, it has almost the same letters. It just lost the first "n", but that's how languages evolve. Now the first mention in English for an orange, I think, is from

the 13th century. So that's the first time that the word came in English. Before traveling traders started bringing oranges to English-speaking countries, there actually wasn't a word for the color orange. The word for orange in English is the word for the fruit. And once people started seeing oranges in markets and knowing what they were, that's when they started using the same word for the color.

It's so amazing that a discussion about fruit can turn into a conversation about language, history, and culture. Thanks so much to Fernando Alvarez at the University of Florida's Southwest Florida Research and Education Center for sharing his expertise on citrus with us.

That's it for this episode. If you have a question about anything, have an adult record it. It's easy to do on a smartphone using an app like Voice Memos or Voice Recorder. Then email the audio file to questions at butwhykids.org. Be sure to include your first name, hometown, and your age. We can't answer every question we get, but we do listen to all of them, and we're always delighted to hear what's on your mind.

But Why is produced at Vermont Public and distributed by PRX. Our team includes Melody Beaudet, Kiana Haskin, and me, Jane Lindholm. Our theme music is by Luke Reynolds. We'll be back in two weeks with an all-new episode. Until then, stay curious. From PRX.