Botany Blog Plants of the Northeastern U.S.

Flowers can be characterized based on the position of the ovary in relation to the other parts of the flower. When the floral parts arise from a position below the ovary, the flower is said to be hypogynous (hypo=below; gynous=female) and the ovary superior since it is above the point where the other floral parts are inserted. When the floral parts arise from a position above the ovary, the flower is said to be epigynous (epi=above) and the ovary inferior since it is below where the other floral parts are inserted.

There is another, special case of an inferior ovary where the bottom of the sepals, petals, and stamens are fused into a cup around the ovary called a hypanthium, or floral cup. Such a flower is termed perigynous (peri=around), because the hypanthium surrounds the ovary. The presence of a hypanthium is a characteristic feature of some families of plants, particularly the Rosaceae and Grossulariaceae. I had a few minutes to kill today and decided to dissect a hyacinth flower that was in the lab and to my surprise found that Hyacinthus orientalis also has a perigynous flower. Here is a closeup of an entire flower

Flower cut in half longitudinally (below)

One last image after the ovary was removed so that the insertion of the stamens at the top of the hypanthium is more clearly visible. Also note the drop of nectar near the base of one of the filaments.

I have been experimenting with creating videos of plants lately. This one was shot using a webcam and it worked reasonably well.

This is an example of a nastic response to a stimulus. Specifically it is thigmonasty, a non-directional response to touch or vibration. The leaf of a venus flytrap is divided into two lobes, each of which bears three trichomes (hair-like structures). The closing of the “trap” is triggered by touching one of the little trigger hairs twice or by hitting two of them in succession. Somehow this causes a change in turgor pressure in the cells of the leaf and a rapid change in shape, allowing the trap to close rapidly.

Plant cells rely on internal hydrostatic pressure to maintain their shape. This pressure is maintained by a relatively high solute concentration inside the vacuole, which results in the absorption of water from outside the cell via osmosis (Raven et al., 2007). As the vacuole swells with water, the protoplast increases in size and the plasma membrane pushes up against the inside of the cell wall, resulting in turgor pressure. The turgor pressure is counteracted by the call wall and these opposing forces help maintain the shape of the cell and ultimately support herbaceous plant tissues.

The image below show cells in a leaf of Elodea canadensis that was placed in a solution of distilled water. The small green structures are the chloroplasts inside the cells and notice that they are distributed near the cell wall.

Elodea cell in a solution of distilled water

If a plant does not receive sufficient water or is placed in environment that is hypertonic (one that has a higher solution concentration than the plant cells, e.g. a salty environment), than the cells will lose water and the plants will wilt. This is because water will be drawn out of the vacuole through osmosis, the protoplast will shrink, and the plasma membrane will actually pull away from the cell wall (plasmolysis), resulting in a loss of turgor pressure.

The following image shows an Elodea leaf that was placed in a 20% sucrose (sugar) solution. Note how the inside of the cell is shrinking and the gap between the plasma membrane and the cell wall (the cell wall does not shrink because it is somewhat rigid due to the presence of cellulose microfibrils).

 Elodea cell in a solution of 20% sucrose

Literature Cited

Raven, P.H., Evert, R.F., and S.E. Eichhorn. 2007. Biology of Plants, 7th ed. Worth Publishers, Inc., NY.

This image is of a Compass Plant (Silphium laciniatum) growing in a prairie restoration in northeastern IL.

One of my favorite books is the Sand County Almanac by Aldo Leopold. It was required reading for a course that I took at community college. This was one of those rare times when, rather than finding it a chore to read an assigned text, I thoroughly enjoyed the book and even read the chapters that were not required for the course. I have read it again several times since. At the time I did not know many of the plants described in Leopold’s essays, but I found the descriptions colorful non-the-less. Having since lived in the Midwest and studied botany there for many years, I can now appreciate the book even more. I would like to share here an excerpt from that book about Silphiums, which are robust, deep-rooted perennials often found in prairies and easy to grow in a sunny garden. Leopold wrote:

“Heretofore unreachable by sythe or mower, this yard-square relic of original Wisconsin gives birth, each July, to a man-high stalk of compass plant or cutleaf Silphium, spangled with saucer-sized yellow blooms resembling sunflowers. It is the sole remnant of this plant along this highway, and perhaps the sole remnant in the western half of our county. What a thousand acres of Silphiums looked like when they tickled the bellies of the buffalo is a question never again to be answered, and perhaps not even asked.

This year I found the Silphium in first bloom on 24 July, a week later than usual; during the last six years the average date was 15 July. When I passed the graveyard again on 3 August, the fence had been removed by a road crew, and the Silphium cut. It is easy now to predict the future; for a few years my Silphium will try in vain to rise above the mowing machine, and then it will die. With it will die the prairie epoch.

The Highway Department says that 100,000 cars pass yearly over this route during the three summer months when the Silphium is in bloom. In them must ride at least 100,000 people who have ‘taken’ what is called history, and perhaps 25,000 who have ‘taken’ what is called botany. Yet I doubt whether a dozen have seen the Silphium, and of these hardly one will notice its demise. If I were to tell a preacher of the adjoining church that the road crew has been burning history books in his cemetery, under the guise of mowing weeds, he would be amazed and uncomprehending. How could a weed be a book?

This is one little episode in the funeral of the native flora, which in turn is one episode in the funeral of the floras of the world. Mechanized man, oblivious of floras, is proud of his progress in cleaning up the landscape on which, willy-nilly, he must live out his days. It might be wise to prohibit at once all teaching of real botany and real history, lest some future citizen suffer qualms about the floristic price of his good life.”

While these plants are easy to grow, they have very deep taproots making them nearly impossible to transplant. The best way to grow them is by directly sowing the seeds. It usually takes two or three years for them to reach sufficient size to bloom, and several more to reach their full potential. Besides Compass Plant, other species include Prairie Dock (Silphium terebinthinaceum), Rosin Weed (Silphium integrifolium), and Cup Plant (Silphium perfoliatum).

It is fall now and the leaves are just beginning to change. On a recent visit to a local research station I snapped this picture of a softball-sized, spiny fruit of what was likely a hybrid between Chinese Chestnut (Castanea mollissima) and American Chestnut (Castanea dentata). I think it was a hybrid as the leaves did not appear downy underneath (as is typical of Chinese Chestnut) but the spines of the fruit are rather thick (they would be thinner in American Chestnut). If one could go back in time, a little over 100 years ago one would find the forests of the northeast were dominated by the American Chestnut. The smooth, brown seeds found inside these spiny capsules were an important winter food source for early settlers and also for wildlife. Today it is rare to find one of these trees and even rarer to find one that bares fruit.

It took only 50 years following the introduction of Chestnut Blight (Cryphonectria parasitica) to decimate the American Chestnut throughout its range. Virtually all trees were killed back to the ground and only a few survivors exists today as “living stumps”. Occasionally a tree may be found that has obtained sufficient size in order to produce fruit. Trees have been planted outside the native range and are important sources of seed for ongoing research to develop resistance to the disease.

There are two main techniques that researchers are currently using to develop blight-resistant American Chestnut. One is the development of hybrids with Chinese Chestnut, which ironically was the host which carried the blight to North America in the first place. Hybrids are then back-crossed with American Chestnut in an effort to reduce the percentage of Chinese Chestnut traits while maintaining blight resistance. The other technique being utilized is genetic engineering; researchers attempt to add specific genes to provide blight resistance to pure American Chestnut.