"The Gymnosperm That Could"
a biography by Prashant Maddineni
external image canadianhemlock.gif

Classification/Diagnostic Characteristics:

Within the two major groups of seed-producing plants lie the gymnosperms, a seed-bearing organism. Named aptly so, gymnosperm, which literally means "naked-seeded" are plants that produce seeds and ovules without a protective ovary or tissue. Divided into four major categories, they remain second to angiosperms in their dominance of the terrestrial environment. Cycads, which are the palmlike trees often seen in the tropic and subtropic areas of the world. If placed on a cladogram of all four species, the cycads would be the earliest to diverge from the rest. About 300 known species exist, many of which grow to over 20 meters tall. Distinct to the cycads, many produce a special tissue that, if ingested, are lethal to humans due to the toxins present. Ginkgos, a common species during the Mesozoic time period, are represented by a single species called the [[#|ginkgo biloba]]. Gnetophytes are desert sprawled organisms characterized by two, long strap-like leaves that cover almost 3 feet. They also share certain characteristics parallel to angiosperms, the other major group of seed-producing plants. Conifers are by far the most abundant of the gymnosperms, and represent the hemlock tree. There remains about 700 species of these cone-bearing trees, and include such as pines and redwoods (1).

Growing between sixty and seventy feet tall, the hemlock tree is a conical conifer with long, slender branches that droop to the ground. Extremely tolerant of shade, the hemlock tree possesses flat and flexible needles with rounded tips. The needles spread in two rows from short leafstalks and are dark green above, with two narrow white bands on the underside. In addition, the hemlock tree has flexible, finely haired twigs and a cinnamon brown bark with deep furrows that create the sensation of scaly ridges. (Alexander Soloviev)

http://www.yale.edu/fes505b/ehemlock.html

Unlike many other phyla of plants, including angiosperms, those of gymnosperms all emerged from separate clades, and are polyphyletic. (Colin Gray)
http://www.cliffsnotes.com/study_guide/The-Gymnosperm-Phyla.topicArticleId-23791,articleId-23772.html


Relationship to Humans:

The needles of the hemlock tree are often used for tea that humans drink, while the bark of the hemlock tree can be used for leather (due to high concentration of tannic acid) that can be used in furniture and other places. In addition hemlock trees are popular in many gardens all over North America. (Cam) [2]
Additionally, hemlock trees are used for timber, despite the wood being hard and brittle.

The wood of Hemlock trees is very popular for [[#|making furniture]] and architectural fixtures because of it's even grain and resistance to scraping. (GC)
[3]

Many Cycad variants produce toxins dangerous to humans when ingested.[1]

Depending on the type of hemlock tree, they can also be used for lumber and floor paneling. A specific type of hemlock tree, the Western Hemlock Tree also contains a very valuable fiber in alpha cellulose fiber that helps in the production of plastic and cellophane.-http://www.gardenguides.com/115414-hemlock-tree.html

The Pacific coast Native Americans used Western hemlocks for a variety of purposes. The bark was used to tan hides as it contains a high concentration of tannins. The bark was also used in the making of dyes for fishing nets, baskets, and paddles. Western hemlock wood is a very durable material and was carved into spoons, bowls, combs, spearshafts, bows for children, and hooks. The branches of the tree were used as bedding material as well as a way to collect salmon spawn from streams. Medicines were also made from parts of the tree such as a bark steeped tea used to treat internal injuries and hemorrages and the use of pitch to treat sunburns and for poultices.
Taken from the website:
http://www.helium.com/items/2109232-tree-profiles-western-hemlock


Habitat/Niche:

Gymnosperms have been around around since the Permian period, a period distinguished my markedly higher temperatures and arid climate. With these sort of conditions present, the conifers and cycads flourished. Going through ecological succession, gymnosperm ridden forests flourished as the group as a whole evolved. They continued to dominate the Mesozoic era, during which Pangea split apart and dinosaurs roamed the Earth. They were the keystone species of trees until approximately 65 million years ago when other plant types began to evolve. Even today though, they [[#|continue]] to dominate many forests, especially ones at a higher latitudes and altitudes(1).

Species of the Tsuga(Hemlock Tree) today are relatively native to moist climates where water stresses are minimal. They are also better adapted to cope with winter snowfalls and ice storms than most trees.
(http://www.conifers.org/pi/Tsuga.php)

Hemlock can be found in regions spanning from Nova Scotia to southern Quebec and Minnesota to Ontario. They can also be found scattered along the Appalachian Mountain and down south as far as Georgia and Alabama. Some botanists have even recognized certain species of hemlock in Asia and Japan. (2) [GW]

Predator Avoidance:

Some gymnosperms, specifically the Cycads, produce a specific type of tissue that, through evolutionary means, has acted as a defense mechanism towards potential predators. When ingested, the tissue of the Cycad release special toxins and neurotransmitters that are potentially lethal when eaten (1).
The Hemlock has been slowly decreasing in population as a result of their destruction by the hemlock woolly adelgid (HWA). The hemlock has relatively no defensive mechanisms to repel this pest, and relies on human management in many cases to maintain populations in many areas.
http://nrs.fs.fed.us/pubs/gtr/gtr_ne267/gtr_ne267_005.pdf

Nutrient Acquisition:

Gymnosperms contain a special water-conducting valve called the tracheid, which is a special water conducting valve of cells within the xylem. They lack more advanced and complex cells found in angiosperms, leading to believe that gymnosperms are potentially farther away from the angiosperms on a cladogram. While a relatively simple and not highly efficient function, the tracheid serves in some of the largest trees known, such as the coastal redwood of California (1).

Although different hemlock systems have different root systems, the two most common are taproot and fibrous roots.Taproots dig deep into the soil to retain nutrients and it is a thick root with tiny roots branching off of it. Fibrous roots on the other hand are generally smaller, more constant-sized roots that grow horizontally or vertically into the soil no matter where they sprout from (can be on any part of plant in soil versus with a taproot). Fibrous roots seem to grow to lesser depths within the ground, but cover a larger surface area, for they grow quickly, and thus can obtain a good amount of nutrients. (http://www.ehow.com/info_8027547_root-system-hemlock-trees.html)

Reproduction and Life Cycle:

In all gymnosperms, the primary structure of reproduction are the conifers, located for the male and female in their respective cones. The female cone is known as the megastrobilus, protected by a modification of branches surrounding the structure while the much smaller male cone is known as the microstrobilus, surrounded by modified leaves for protection.
Reproduction starts when the male gametes are created in the form of pollen grains, which in turn frees the plant from its dependance on liquid water for fertilization. Wind carries these grains to the female gamete inside a cone. A pollen tube allows for the sperm to travel through the tissue of the cone to the female gamete, where it released two additional sperms where one of which disintegrates after it unites with the egg.
Most conifer ovules, the stage preceding the transformation into a seed after fertilization, are born with scales protecting them by clustering tightly about the ovule. Other gymnosperms have tightly closed cones that release the seeds only with the presence of fire to split them open. Other conifer species have a soft, berry-like tissue that forms an envelop over the seed. Animals eat this berry-like structure and carry them away from the parent plant, before releasing them through droppings (1).

external image hemlock%20w.%20a.%20lifecycle%20copy.gif
This image shows the lifecycle of a hemlock tree along with the time of year that the tree grows from one stage of its life cycle to the next.
Because Hemlock trees live for a very long time, they have vast relationships with the organisms around them. For example, when the hemlock tree gets its roots in the ground, they will establish an intimate relationship with many fungi. The tree can grow up to 100 feet tall and live to be more than 150 years old.
http://www.opalcreek.org/history-ecology/life-and-death-of-a-western-hemlock/ (BHu)
external image th?id=I.4661380355392540&pid=15.1

Growth and Development:

Hemlocks like the Canadian Hemlock can reach heights between 50 to 70 feet and a width that ranges from 25 to 35 feet. Hemlocks in general grow very well in acidic soil (that is soil with a low pH), that is well drained. Hemlocks also require full sun; sun throughout the entire span of the day.
http://www.arborday.org/treeguide/TreeDetail.cfm?id=142

Integument:


In the megasporangium, the area where the female gamete will eventually be formed, lies an enclosed layer of sporophytic tissue that will eventually develop into the seed coat that protects the embryo. Known as the "integument, it constitutes the ovule with the tissue attaching it to the maternal sporophyte, through which pollen will soon enter through the tip of the tissue by the wind, called the micropyle (1).

Hemlock trees have a red brown back covering. In young trees the back is a fine covering while in more mature trees it is more rough, broad, and furrowed. It has green needles that are about 1-1.5 centimeters long. Also, the cones are about 1.5 to 2 centimeters, and the buds are .5 centimeters.
http://www.lrconline.com/Extension_Notes_English/pdf/hmlck.pdf


Movement:



The hemlock produces both pollen cones and seed cones on the same tree. Pollen cones occur near the tips of leafy twigs, while seed cones occur at the tips of such twigs. Although the tree does not move, the seeds from the tree will disperse with the help of outside forces such as gravity, wind, animals, and water. The seeds will disperse to new locations so that the new seeds will not accumulate in one area.
http://www.illinoiswildflowers.info/trees/plants/east_hemlock.htm


Sensing the Environment:
Phototropism is directional growth in which the direction of growth is determined by the direction of the light source. In other words, it is the growth and response to a light stimulus. Phototropism is most often observed in plants
http://en.wikipedia.org/wiki/Phototropism
Gas Exchange:

The needles on hemlocks dark green along the top and are a paler shade on the bottom; the pale strip is actually a line of stomata that open and close to mediate gas exchange between the needle and the atmosphere. (2) [GW]

external image images?q=tbn:ANd9GcQ6B3CneyyWmhkUv9rOx-2xn13FfIn3AXbBBYDN28pwDb1uE8XX2Q


Waste Removal:

The hemlock tree removes waste via transpiration and photosynthesis as it releases O2 with the help of lenticells and stomate. They also release water by using hitatodas and gutatodes. (Evan Kates)

(http://www.for.gov.bc.ca/hfd/pubs/docs/sil/Sil469.pdf)


Environment Physiology:
The hemlock tree is found in cool, moist woods and also in many shaded areas. Eastern Hemlock grows best in rich, well-drained soil and is ofte found near other large trees such as maples and pines.

http://www-pub.naz.edu:9000/~treewalk/north_tree_walk/tsuga_canadensis/index.htm


Internal Circulation:

The hemlock tree has a vascular system which transports nutrients and other substances, The vascular system is composed of a phloem and a xylem. The xylem transports, water, and minerals, while the phloem transports food and nutrients through the whole tree.
external image illo-1ketxfd.jpg- Diagram of the xylem and phloem (which compose the vascular system)- http://sarahalizerig.edublogs.org/files/2012/06/illo-1ketxfd.jpg


http://www.diffen.com/difference/Phloem_vs_Xylem



Chemical Control:
Review Questions
1.What are the different types of hemlock trees and what characteristics separate them from eachother?
2. How do Hemlock trees defend themselves against predators if they can not move?

3. How does the stomata play a role in waste removal and gas exchange?
4. How does the internal circulation help make the tree 60-70 feet tall?
5. How does the tree create a protective barrier for the seed that will eventually be formed?


References:
1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price.Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.
2. http://www.gardenguides.com/115414-hemlock-tree.html
3. http://www.for.gov.bc.ca/hfd/library/documents/treebook/westernhemlock.htm