The second part of this chapter, Pages 311-328 is a look at the structure and function of leaves.
The writing starts with a paragraph on some "oh, wow" data about how many leaves are on a plant or planet (pg. 311). While you are on this page, though, please notice the longitudinal section of the onion (Fig. 14.8A). While the purpose of this figure was to show stems below ground, the stem part of the onion is the tiny (about the size of a dime) amber zone just above the roots. Most of the bulb is actually bases of alternate leaves attached to this basal plate (stem). So, when you are eating onion rings, the rings are just the cross sections of leaf bases...no stem there! An onion is mostly leaf!
The text continues with descriptions of how leaves form at the meristem. Please notice the place (page 312) where the leaf primordia are given the fuction "to protect the apical meristem." I hope you will never give that answer on a test...finish it with "against ______", where you fill in the blank with the rest of the description.
Two terms are important to notice and learn (so you can read the text). Adaxial means the upper epidermis, and abaxial means the lower epidermis. To test whether you understand this, read the paragraph about fern leaves (bottom of left column page 312), think about what you have read, and decide about the accuracy of the text here. Think about how the forming leaf becomes coiled in the first place, then how the leaf uncoils. Which process has the author just described...coiling or uncoiling?
Read the section on phyllotaxis, but don't sweat the math (it is easy) but we won't be doing much with it. It is interesting, if you like math, but is more likely a topic for plant physiology. One might ask how you get from the formula on page 313 to the parentheticals in the text. Yeah, something wrong here.
The structural section begins on page 315, and my lecture started there.
Curt, you might notice the last sentence of the first (partial) paragraph on page 317...sound familiar?
At the bottom of page 317 you should read about vein endings. This is the critical area for transpiration and translocation. Not enough is said or written about this place. We could use each one of you to help our understanding of plant physiology in this critical place.
As you read about leaf structure, think about photosynthesis and transpiration. How is the structure related to function? Think about why the phloem is under the xylem instead of above it. When you get to the discussion about C-4 plants (page 319), think about C-4 photosynthesis. Is the structural design of this leaf an efficient way to handle the chemical processing of the C-4 pathway? As this part of Exam I was weak, I'd be expecting a question on this for Exam II.
Notice the sequence of environmental variations Page 320-322. You should be seeing some of these example leaves in lab (or lab makeup) and should be ready for the exam and practical. At the end of this section, there is an interesting paragraph on dimorphic leaves. The physiological connection, the part about abscisic acid causing development of emergent (above water) leaves rather than submergent leaves, is very interesting. Abscisic acid is made when leaves are under drought (water stress) conditions. An exposed meristem would likely make this chemical and change over its leaf production. I bet you can think of a neat independent study project with some of our floating ferns in the greenhouse!
In the section on leaf movements, some of you who went to Bermuda (and/or) Belize should remember headland plants holding their leaf edges (rather than upper epidermis) to the sun to reduce solar heat gain (Sea ox-eye and beach lobelia, etc.). Later in the paragraph it discusses what happens to Rhododendron when it is cold. I think most of you have seen (but maybe not noticed) this phenomenon. It is sometimes called thermonasty but, in my opinion, this response is more likely a response to not only cold but to the low humidity observed at below-freezing temperatures. I wonder if experiments with decent control could distinguish these two variables. There's another winter independent study idea.
The long section on modified leaves gives you some idea how variable leaves are. Leaves, due to such distinctive features, are useful for distinguishing species of plants. Later we will see that the specially modified leaves (sepals, petals, stamens, carpels) of the flower are even more diagnostic.
The section on usefulness of leaves makes interesting reading. Henna is used not only to stain fingernails and cloth for Egyptian mummies, it is also an important dye for hair. It has been used since the days of the pharoahs to add red highlights to dark hair, and to make blonde or gray hair red.
The word, "popular", is hard to interpret. The book describes digitalis and digitoxin as popular. I think I'd use "useful" or maybe "important." Later cocaine is called popular; I think this use of the word is more accurate. Where is the "Epilogue?" Don't you hate it when a book or magazine tells you to find something that's somewhere else that is almost impossible to find? I'm using the paperback version and Epilogue is not listed in either table of contents.
Another little correction, when women used extracts of Atropa belladonna to dilate their pupils, you should notice that the dilated pupils make the eyes look darker rather than "brighter." It is also true that sociology/psychology studies have asked people in modern times to pick out the "most beautiful" portrait photo of a pair of shots taken of one woman. The only difference in the photos is the dilated pupils in one. People overwhelmingly choose the one with the dilated pupils. Now you know why, when you had your senior pictures taken, you were ushered into a semi-dark studio and the photos were taken with electronic flash (too rapid for pupils to constrict).
I hope all you tobacco users will read about the health consequences of your habit. I agree with the author that this is one horrible drug administration method. While the nicotine is addictive but not particularly debilitating, the accompanying tars, aldehydes, and other smoke components are debilitating and even lethal. There has to be a better way to get the nicotine "fix" the addict needs to feel normal. Maybe the patches and chewing gum administration methods are better than the smoke method of administration. It is time for change!
Prescription drugs are horribly expensive. We need change in this area too. Health care costs could be significantly reduced with just a few changes in the Food and Drug Act of 1914. That law took away the freedom of citizens to go to a pharmacist and get the drugs that the citizen, with the advice of the pharmacist, choose to use. Since that time we must first pay for an office visit to a doctor (to have him/her tell you what you already knew was the problem) to get a scribbled permission slip (prescription) to buy the needed drug. This note will cost you (or your insurance premiums) about $75. Then you get to pay the inflated cost of the prescription drug itself. Most-commonly used drugs should be made over-the-counter (OTC=not requiring a prescription). After a child has had a few ear infections, the parent knows what is wrong by the symptoms and knows what drug is needed (amoxycillin). If the physician took a culture and identified the offending bacterium and used a particular antibiotic for that specific bacterium, it would be worth having the required doctor visit. This never happens, however, the doctor simply looks at symptoms and prescribes the same thing every time (after three kids and perhaps 10 pediatricians, believe me, I know). Worse, struggling new parents often don't use up the complete cycle of antibiotic because of the high cost (perhaps $125 total), and hope to save half a bottle for the next episode. This is a health risk because failure to use the whole cycle (10 days) results in selection of antibiotic-resistant strains. If the standard treatment were available OTC at an OTC (competitive) price (maybe $20), health costs to young families would be reasonable and public health-risks reduced! Tell your congressmen to repeal most of the FDA of 1914!
At the end of the chapter (page 328) the author mentions the use of plants as images for sports teams, etc. Please note: sculpt means 3-D but logos are usually 2-D. In fact, for a short time, ECSU was considering using the blue-oak as its "mascot." The oak was deemed a symbol of strength. The state has a history including the famous charter oak. The blue color is our school color. No one could claim that we were offending any gender or ethnic group of humans with a leaf or acorn mascot. Frankly, though, "warrior" is not specific to any ethnic group. There have been warriors in virtually every group of humans in history...and sometimes the warriors were women. Providing we do not use images of ethnic peoples, I see nothing ethnically offensive with "warriors". It is a belligerent image, but then most sports are like a battle anyway.
In the parting remark, the author mentions leaves serving as a source of shade. In addition to air purification and oxygen production, a tree over your house (or on the south side of your house) keeps solar gain down and keeps you cool. The cost is free! No air conditioning costs and concommitant air pollution...just the opposite! Perhaps you have heard my definition of suburbia (sloburbia)...where they knock down all the trees and name the streets after them. If you are building a new house, make sure your contractor knows that s/he is not to knock down the trees that will shade your new house. It will take years to grow a replacement large enough to shade the house. Most contractors prefer to knock down all the trees on the lot for "convenience" or "access" but most of that destruction is completely unnecessary. They can work for a few weeks around the tree so you can enjoy its benefits for your lifetime! Think about it.
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