Why is a grain of corn a fruit while a pea is a seed?
Do these people who call a tomato a fruit know what they are talking about? If a sunflower “seed” is actually a fruit, why?
Distinguishing Between Seed And Fruit
This matter of what is a seed and what is a fruit is really simple if you begin with the flower and watch the pollination process, knowing that inside the pistil, within an ovule, an egg cell is fertilized by a sperm cell.
This location sequence is important – it’s like those egg sets for children where each egg comes apart to reveal a smaller one inside.
From the outside in, the sequence is the ovary portion of the pistil (pea pod, iris capsule, or fleshy part of tomato), then the space within the ovary walls, then the ovules, which are to become the seeds.
These are the peas, the hard round iris seeds, or the seeds of the tomato.
Fruit is a flower’s mature ovary and contains the seeds developed from the fertilized ovules.
This intricate structure, the seed, has evolved around the fertilized egg we mentioned above.
The egg cell becomes the embryo which is embedded within the seed.
The whole purpose of flower, fruit, and seed production is to perpetuate the species, which is done by the embryo.
Delving Into The Corn Plant’s Parts
Let’s take another look at those introductory questions.
Why is a grain of corn a fruit? Have you a roasting ear handy?
A corn plant bears its staminate (male) flowers in the tassel and the female flowers on the ear.
As you peel back the husks, you will see that each strand of silk leads to a single kernel of corn.
Now think what this means in terms of the flower structure we have studied.
Remember that a pistil is made up of three parts. These are:
- The stigma, or pollen-receiving portion
- The style, which connects the stigma to the ovary
- The ovary, the lower portion of the pistil, contains the ovules, which will eventually become fruit.
So the protruding end of the corn silk must be the stigma, the long strand within the husks must be the style, and the kernel must be the ovary.
Who would ever have thought that an immature corn kernel was a highly streamlined female flower?
Of course, in this highly specialized pistil, there is just is single ovule, and when it matures, it fills the ovary space.
The ovary wall becomes thin and horny (the thing that sticks in your teeth when eating popcorn).
So you see that a kernel of corn is a seed tightly enveloped in a much-reduced pistil wall and therefore meets the requirements for fruit.
How About The Peas?
In the case of the pea, you have probably figured out by now that the pod is the ovary of the pistil, and since each pea has developed from an ovule within the ovary, each one is a true seed.
The pea pod as a whole, with seeds enclosed, is a fruit.
Tomato As A Fruit
In the botanical sense, a tomato is really a fruit. It also developed from the ovary portion of a tomato flower pistil.
You can still see the scar of the style and stigma on the bottom of the tomato directly opposite the stem.
In this case, the ovary walls have become fleshy, the ovary spaces are filled with free-floating cells, and the seeds are in clusters on the inner part of the ovary.
You may have also noticed that in the old-fashioned tomatoes, there were five compartments inside. This shows that the tomato has a compound pistil composed of five parts (carpels) fused together.
Modern hybrids have lost this distinct pattern because plant breeders try for a meatier tomato.
Increasing the number of carpels achieves more solid tissue and less juicy space.
Sunflower Seeds
The sunflower “seed” is similar to the grain of corn.
Sunflowers have composite flowers; each strap-shaped “petal” around the edge of the “bloom” is a complete miniature flower, and each of the small divisions in the sunflower’s center is also a special sort of blossom.
A sunflower, then, is actually a whole bouquet of small, highly modified flowers.
The pistil, one of these center blooms, behaves much like the corn pistil and forms a small, seed-like structure composed of a hard, usually striped pistil wall containing a single seed.
Observing Different Seeds and Fruits
Watching withered flowers in the garden can be lots of fun.
Have you seen the dark “bee” in the center of the delphinium blossom gradually develop into the five-part capsule that reveals its buttercup family relationship?
Now think of the seed capsules of your love-in-a-mist, the columbines, the larkspur, anemones, and so many others — aren’t they all similar?
One of the easiest field identification marks of the buttercup family is this matter of unfused or slightly fused carpels of this characteristic capsule shape.
There are technical names for all the different sorts of fruits and the many different sorts of seeds found within the fruits.
You will find this information in any good botany book; studying it is a good club project.
44659 by Dr. John P. Baumgardt