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Growth and Development of

the McIntosh Apple

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Curricular Materials to Accompany the McIntosh Apple Development Poster
Distributed by the Education Committee of the Botanical Society of America
Posted March 2001


Growth and Development in Animals and Plants

 Let's think about growth and development in animals and plants. Are most animals, including humans, born with all their parts? Certainly the various parts of a baby animal are not all the same size they will be in the adult. Nor are they in the same proportion as in the adult. Which parts of a baby human are relatively large? Which are relatively small? As the baby grows, the parts enlarge slowly and at different rates until they reach the size of the typical adult.

 Do plants grow in the same way? Think about a plant that has just emerged from a seed... a young seedling. Does it have a root? Does it have leaves? Does it have a stem? Yes, it has all of these parts although not as many as when it is an adult plant nor are the parts as large as they eventually will become. But some parts of an adult plant are totally missing from the seedling. Are there flowers? Are there fruits? Are there seeds? No, these parts are produced much later, after the stems, roots, and leaves have developed more fully.

 We see from this brief discussion that animals and plants develop quite differently. Watching plants develop flowers, fruits, and seeds can be very interesting. We can learn where these parts are produced and we can watch them grow into fully functional organs. We can think about what factors might be necessary to trigger the full development from flower to fruit to seed.

Apple Development

This poster shows the development of the McIntosh apple beginning in late Winter when the stem tips or "buds" are still in their dormant condition (1). In early Spring each bud begins to swell and turn green, bending back the tough bud scales (2). Continued growth expands the bud still more (3)!  Gradually the fresh young leaves open (4), and expand into the typical shape and size of apple leaves (5). Several additional days of growth allow the tightly closed, hairy flower buds in the center to be visible (6). The flower buds    continue to swell (7) as the parts inside the bud are growing. Notice the difference between the red parts (the petals), and the five green, hairy parts (the sepals), surrounding the petals (8).  Through the next stages of development (9 and 10) we see the individual flower stalks getting longer and the flower buds swelling more and more.  Finally one of the flowers bursts open (11) revealing the parts inside.  The petals are white on the inside with a tinge of pink on the outside!

The stamens flare out from the center (12) and we can see their nearly white stalks (filaments) each topped with a tiny yellow anther which contains pollen.  Even though we cannot see it, there is sweet nectar at the base of the petals and the apple blossoms will be visited by honey bees that gather the nectar then carry it to their hives to produce honey.  While gathering the nectar, the bees move the pollen from one tree to the blossoms of another tree where they rub it on another structure in the center of the flower, the stigmas on the very tip of a long styles that are attached to an ovary far below the attachment point of the petals. The movement of this pollen is called "pollination" and without it the fruit and the seeds would not develop on the apple tree.  After shedding their pollen, the anthers darken and begin to shrivel up while the petals begin to wilt (13), and if we look closely, we can see the stigma, the pronged structure in the center of the blossom where the pollen was deposited.  Soon the petals will fall off (14) and if you were in the the apple orchard at this time, you might think the thousands of petals drifting through the air look like falling snow!  Notice that the small green sepals are still attached.

Now the ovary begins to enlarge (15), turning the sepals upright from their former flared position. We can see the stamens beginning to shrivel and dry up. The fruit begins to enlarge very rapidly below the sepals which stay the same size as always but seem to be getting smaller by comparison (16).  The apple is fuzzy at this stage (17) from a covering of very soft hairs and the stamens are continuing to dry up and disappear beneath the enfolding sepals. After several weeks the soft hairs disappear from the surface of the developing fruit which looks more and more like an apple (18). Summer sun and rain allows the apple tree to produce lots of sugarwhich it can store in the expanding apples. The added weight of the growing apple causes it to hang down (19) and the cool, sunny days of Autumn bring a blending of nice hues of red and yellow to the skin of the apple.  Can you see evidence that the parts of the apple exposed to the sun will turn red and any of the fruit that is shaded will be yellowish green?  Cells inside the apple are alive and need oxygen to stay alive. The small white "dots" on the surface of the apple allow oxygen to pass through the skin which otherwise has a waxy coating to keep the fruit from losing too much moisture.

Now the fruit is ripe and ready for us to pick!  If we cut the fruit lengthwise, we will see that there are seeds inside (20)!  They are in what we call the "core" of the apple.  Notice that the stalk of the flower is now the stalk of the fruit and is at the top.  Looking carefully at the bottom of the apple, we can find the five sepals of the flower forming a star-like pattern.  If we gently pry up the sepals we will see some of the dried, shriveled stamens underneath!  Animals, such as horses and deer, are attracted by the odor of the ripening apples and love to eat them. After eating the apples the animals wander far away.  The seeds are able to withstand the journey through the animal's digestive track and are eventually "planted" when the animal eliminates waste. By now the seeds are far from the parent tree and, when the seeds germinate next Spring, their seedlings will be the first of a new grove of apple trees!  Apple trees use their flowers to make more apple trees!

 

Pomology

Growing apples is a very serious task. The orchardist must rely on advice from researchers (pomologists) who develop new varieties of apples through selection or plant breeding and who discover the need for various fertilizers to help the trees to produce large crops of apples. Unfortunately, apple trees have pests! Some are fungal diseases and others are insect pests. Researchers determine which chemicals are effective against the various pests and can tell the apple grower exactly when to apply each kind of chemical. It's not as simple as it might seem! For example, if there are insect pests, it is important to apply chemicals at a time that will kill the pests without killing the bees that are essential for pollination.

 To assist in the application of these chemicals, pomologists have given names to the various developmental stages of the apple. They can use these terms to describe the right time to spray chemicals to the exact day or even the exact hour! Here are the terms applied to the stages on the poster:

  1. silver tip
  2. green tip
  3. quarter-inch green
  4. half-inch green
  5. tight cluster
  6. pink tip - king bloom (center blossom)
  7. pink tip - full
  8. open cluster
  9. showing first white
  10. popcorn
  11. king blossom open
  12. full bloom
  13. petal wilt
  14. petal fall
  15. fruit set
  16. half-inch fruit
  17. 1-inch fruit
  18. mid-summer
  19. mature fruit
  20. mature fruit (longitudinal section)

 

History of the McIntosh Apple

 How did the McIntosh apple first come into cultivation? John McIntosh, whose parents had immigrated from Inverness, Scotland, lived in the Mohawk Valley of upstate New York in the 1770's. When the Revolutionary War spread to his area, John, who sympathized with the British, moved north to Dundas County, Ontario, Canada. He was clearing some land on his new farm when he discovered some apple seedlings which he transplanted. Only one survived and it produced delicious red apples, McInstosh Reds. John and his son Allen and, later, his grandson Harvey propagated many new trees from cuttings of the one original tree which bore fruit until 1908 and died in 1910. By the middle of the 20th Century, the McIntosh apple was a favorite apple of North America, accounting for 40% of the Canadian apple crop in the 1960's.

Historical Research: A Class Project

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