Wikipedia:Reference desk/Archives/Science/2014 March 19

= March 19 =

What is the scientific consensus or emerging consensus about whether homosexuals and bisexuals were born that way?
Like the science behind man-driven climate change, the science of same sex attraction is a controversial one. With the issue of gay rights heating up more and more in the U.S and around the world, I've started searching on the subject of homosexuality as most people now are. It still seems that the science of it is all over the place on that with some scientists saying that there's no conclusive evidence yet that homosexuals and bisexuals were born that way or not and other scientists saying that there's conclusive evidence homosexuals were born that way or not. Some scientists even question whether there are really homosexual non-human animals at all, if it is based upon instincts or if it is actual homosexual activity. Also, some people who go to one gender jails seem to get into same sex relations, appearing to show that at least some LGB weren't born that way, which confuses me. I don't know if some of the MSNBC Lockup episodes are accurate, but that's what they show. Willminator (talk) 04:35, 19 March 2014 (UTC)
 * See Homosexuality, Biology and sexual orientation, Environment and sexual orientation and Homosexual behavior in animals. Also, you can't conclude that a straight person who starts having a same-sex relationship for the first time in prison has changed their sexual preference.  They may still have a strong preference for an opposite-sex relationship, but that's completely unavailable, so they're just resorting to a same-sex relationship as something that's at least somewhat preferable to no sex at all.  A lot of MSM in prison aren't even willing participants; see Prison rape and Prison sexuality.  Red Act (talk) 06:02, 19 March 2014 (UTC)
 * In some cultures other than the current Western conception, there's a notable difference in that while Two-Spirits and hijras/kothis take on a more or less homosexual identity, there are also a large number of ordinary "heterosexual" men who have sex with them - to the point where it seems like sex within the homosexual group may be the rarer relation! (I wonder if part of this cultural difference has to do with the oppression of homosexuals in Western cultures until after birth control had become available, which freed heterosexual women to have casual sex?) Wnt (talk) 11:32, 19 March 2014 (UTC)
 * From the second paragraph of our article on Homosexuality: "There is no consensus among scientists about why a person develops a particular sexual orientation...". The entire article is well worth reading. In practical terms, human sexual behaviour is so complex that a full explanation is probably not yet within our grasp. RomanSpa (talk) 14:41, 19 March 2014 (UTC)
 * But is there a scientific consensus or emerging scientific consensus on whether or not homosexuality and bisexuality is an inborn trait some people have? What does it mean by "develop?" The second paragraph makes it sound, but not clear enough, as if the scientific consensus is that homosexuality is something people are not born with, but that is developed some time in life. The emerging consensus in the non-scientific world is that homosexuality is an inborn trait according to the polls. Willminator (talk) 02:41, 20 March 2014 (UTC)
 * No, the word "develop" does not at all necessarily imply that the trait isn't inborn. Many human traits develop before birth, i.e., develop during prenatal development.  And the second half of the sentence that RomanSpa half quoted is important: "... however, biologically-based theories for the cause of sexual orientation are favored by experts, which point to genetic factors, the early uterine environment, or both in combination."  I.e., although there isn't a consensus on the matter yet, experts on the subject currently favor the idea of homosexuality being caused by one's genes (which are determined at the time of conception, which occurs before you're born) and/or early uterine environment (which is something that you're only exposed to before you're born).  I.e., the emerging consensus in the non-scientific world that homosexuality is an inborn trait is consistent with current scientific understanding.  Red Act (talk) 05:18, 20 March 2014 (UTC)


 * They knew something was up with me when I made a pass at both the the doctor and the nurse. μηδείς (talk) 23:22, 19 March 2014 (UTC)


 * Uh oh, serious gender stereotyping there. Richard Avery (talk) 08:22, 20 March 2014 (UTC)
 * Yes, I was born back in the day when people took their gender stereotypes seriously. μηδείς (talk) 16:55, 20 March 2014 (UTC)
 * Richard is being sexist if he associates doctor with a man, and nurse with a female. Imagine the plot twist: the doctor was a woman, the nurse a man, Medeis' comment still makes sense.  — Preceding unsigned comment added by 185.13.202.241 (talk) 20:29, 20 March 2014 (UTC)
 * Supongo que puedo creer por su orígen que tu comentario fue acto de vandalismo?


 * Did you likewise call on the lady with the alligator purse? If you don't know that reference, then just skip it. Or even if you do. ←Baseball Bugs What's up, Doc? carrots→ 00:53, 20 March 2014 (UTC)
 * Age of search engines. Wnt (talk) 02:34, 20 March 2014 (UTC)
 * I take it this is to the same tune as Miss Susie? But it's a much less interesting song. --Trovatore (talk) 08:05, 21 March 2014 (UTC)

Smoking alcohol - how does this work (if it does)?
As demonstrated by YouTube's famous LA Beast. The pump is somehow making the alcohol come out of the drink and into vapour form? How does this work - assuming that the Beast isn't messing with us for the lulz. I should probably say that I have no intention of trying this - and neither should any of you. --Kurt Shaped Box (talk) 14:50, 19 March 2014 (UTC)


 * We have an article about Alcohol_inhalation. I recall seeing novelty shops selling vapor by the minute out of a kiosk in a few US airports, back in the aughts. SemanticMantis (talk) 14:57, 19 March 2014 (UTC)


 * Alcohol vaporizes at a lower temperature than water, so heating it is one method to draw off the alcohol vapors (think cherries jubilee or bananas foster). I believe lowering the pressure might work, too, but somebody else will need to confirm that. StuRat (talk) 20:09, 19 March 2014 (UTC)


 * Besides the question of, "What do you expect it to do when you light it?" there's the issue that ethanol is a noxious, dessicating, toxin. We drink it in very diluted fashion, and still it kills the strongest of humans.  Spiking an IV drip sounds better than inhaling alcohol fumes.  Even a vodka enema. μηδείς (talk) 23:20, 19 March 2014 (UTC)


 * Those alcohol fumes are probably quite dilute, too (a low partial pressure in air). StuRat (talk) 05:12, 20 March 2014 (UTC)


 * A vodka enema, now that could kill you in short order. 24.5.122.13 (talk) 05:48, 20 March 2014 (UTC)


 * I suppose I didn't mean the volume that implies. More like a suppository vokda shooter. μηδείς (talk) 16:53, 20 March 2014 (UTC)


 * Yeah, but Beast has bigger arms than Christopher Hitchens. How does the bike pump thing he's doing specifically work though - anyone know? --Kurt Shaped Box (talk) 11:06, 20 March 2014 (UTC)


 * Sure sounds like it's lowering the pressure to draw the alcohol fumes out. StuRat (talk) 01:37, 22 March 2014 (UTC)

Secondary alkyl halides do not undergo SN1/ E1 reactions?
According to the latest edition of Bruice's organic chemistry textbook, recent research has found that "Secondary alkyl halides do not undergo SN1/ E1 reactions" (source: see here and click on "new to this edition"). Is this true? Can someone find me a peer-reviewed paper about this? How come scientists didn't notice this before?--FutureTrillionaire (talk) 18:17, 19 March 2014 (UTC)
 * I have that actual Bruice book, and the SN1 section on p417 cites this claim to
 * The current (and previous) McMurry organic chemistry text gives relative SN1 reactivity of 1,000,000:1 2-methyl-2-bromopropane:2-bromopropane, and only mention 3° (and allylic/benzylic) but not simple 2° alkyl halides as common SN1 substrates in the SN1/SN2/E1/E2 reaction comparison summary, so I'm not sure this is really strictly "recent research", so much as making explicit a blanket "not 2°" rather than "2° possible but so very much slower than 3° that may or may not be viable" that may have been commonly taught. I don't have a previous edition of Bruice handy to see what they do/don't claim for possibilities or rates. The current McMurry (copyright 2012) gives specific example of E1 of a menthyl chloride, a 2° halide, using its product distribution to verify that mechanism vs E2, whereas the current Bruice only discusses the E2 possibility of it (in keeping with its basic claim that 2° C+ are too unstable to be a viable intermediate). DMacks (talk) 19:03, 19 March 2014 (UTC)
 * That Murphy paper makes a strong case for "no SN1 at 2° alkyl halide", including explaining the apparent racemization during substitution of these substrates (the typical observation used to support SN1 rather than SN2 as the mechanism) based on an alternate pathway involving (possibly repeated) successive SN2 steps. The article does not mention elimination., and a quick glance at the elimination chapter only refers back to the substitution chapter as the basis for ruling out E1 of 2° halides based on the "relatively unstable carbocations" that would be required (p456–457). DMacks (talk) 19:19, 19 March 2014 (UTC)
 * Thank you for the explanation! I have the 6th edition of the Bruice textbook, and it says in a chart that 2° alkyl halides undergo both SN1 and SN2. Also it has a chart that looks something like this:
 * {| class="wikitable"
 * {| class="wikitable"

! alkyl bromide !! class !! relative rate
 * tert-butyl bromide || 3° || 1,200,000
 * sec-propyl bromide || 2° || 11.6
 * ethyl bromide || 1° || 1.00
 * }
 * I think you're right that in the 7th edition, Bruice decided that the rate of 2° is negligible compared with 3°. However, does this mean that we can't perform a SN1 reaction using a 2° alkyl halide in real life?--FutureTrillionaire (talk) 20:44, 19 March 2014 (UTC)
 * The problem with that is, for secondary alkyl halides the SN2 (or E2) reactions are so much more favorable that you'd have a hard time forcing the stuff to undergo an SN1 reaction instead. 24.5.122.13 (talk) 23:18, 19 March 2014 (UTC)
 * It is also very important to remember that these are not either/or propositions. It's better to think about the SN1/SN2/E1/E2 as a "continuum" rather than a set of choices.  You're likely to get actual products from all 4 mechanisms in just about every nucleophilic reaction (at least a few molecules!) the question is how a set of reaction conditions (including the structure of the nucleophile, the structure of the electrophile, the nature of the solvent, the temperature, the relative concentrations, etc. etc. etc.) will result in a particular distribution of mechanisms.  It isn't correct to think "Tertiary bromides don't undergo SN2/E2 reactions ever"  It's better to say "unimolecular mechanisms dominate the reaction of tertiary alkyl halides" for various reasons (stability of carbocation; steric interference at the attack site, planar attach site in the carbocation, etc. etc.)  The problem always comes at the edge cases; how much better does an SN1 mechanism have to dominate a reaction for it to be the dominant reaction type?  Is a 51/49 ratio enough?  80/20?  95/5?  99/1?  How much does one mechanism have to dominate the reaction for us to say that the other mechanisms aren't happening to a significant extent.  The problem may likely come from different chemists looking at the same set of data and arriving at different definitions of "enough".  -- Jayron  32  02:55, 20 March 2014 (UTC)
 * I think you're right that in the 7th edition, Bruice decided that the rate of 2° is negligible compared with 3°. However, does this mean that we can't perform a SN1 reaction using a 2° alkyl halide in real life?--FutureTrillionaire (talk) 20:44, 19 March 2014 (UTC)
 * The problem with that is, for secondary alkyl halides the SN2 (or E2) reactions are so much more favorable that you'd have a hard time forcing the stuff to undergo an SN1 reaction instead. 24.5.122.13 (talk) 23:18, 19 March 2014 (UTC)
 * It is also very important to remember that these are not either/or propositions. It's better to think about the SN1/SN2/E1/E2 as a "continuum" rather than a set of choices.  You're likely to get actual products from all 4 mechanisms in just about every nucleophilic reaction (at least a few molecules!) the question is how a set of reaction conditions (including the structure of the nucleophile, the structure of the electrophile, the nature of the solvent, the temperature, the relative concentrations, etc. etc. etc.) will result in a particular distribution of mechanisms.  It isn't correct to think "Tertiary bromides don't undergo SN2/E2 reactions ever"  It's better to say "unimolecular mechanisms dominate the reaction of tertiary alkyl halides" for various reasons (stability of carbocation; steric interference at the attack site, planar attach site in the carbocation, etc. etc.)  The problem always comes at the edge cases; how much better does an SN1 mechanism have to dominate a reaction for it to be the dominant reaction type?  Is a 51/49 ratio enough?  80/20?  95/5?  99/1?  How much does one mechanism have to dominate the reaction for us to say that the other mechanisms aren't happening to a significant extent.  The problem may likely come from different chemists looking at the same set of data and arriving at different definitions of "enough".  -- Jayron  32  02:55, 20 March 2014 (UTC)

How to refer to an antibiotic which is used to select against eukaryotic cells?
Puromycin is an antibiotic. It is effective against microbes and can also kill and be used for selection against unprotected eukaryotic cells. When it's activity against microbes is immaterial how can I refer to it? A "selective agent" or still as an antibiotic? --129.215.47.59 (talk) 18:35, 19 March 2014 (UTC)


 * When in doubt, specify, especially if this is for research or academic writing. E.g. "We used Puromycin, an antibiotic which was chosen for this purpose because of its selective properties when applied to eukaryotic cells. In this application Puryomycin acts to ...[kill some and leave others, based on some property]([citation])" Once you've specified, you can even set up a shorter term for later use, E.g "...(henceforth, 'selctive agent')." SemanticMantis (talk) 19:25, 19 March 2014 (UTC)


 * The term biocide also applies, but I think the solution above is more plausible to read in a real paper. Wnt (talk) 22:27, 19 March 2014 (UTC)


 * Given the terse style often used in papers (often the result of publishers' word limits), I would expect something very brief like "Puromycin was used for selection of [whatever] under [some conditions] ([citation],[citation])" in the materials and methods, and selection agent or just plain puromycin elsewhere (the latter having the twin advantages of being both more specific and shorter). The expert reader will already know that puromycin is widely used as a selection agent, and will pretty much assume that is its role if it shows up in eukaryotic culture.  (Pull the full text of some papers mentioning puromycin to see lots of examples.) TenOfAllTrades(talk) 22:59, 19 March 2014 (UTC)


 * Alright, sociology experiment: Free hits for puromycin selection pull up: "podocyte toxin"  "widely used drug/selection marker/protein synthesis inhibitor"  only "puromycin selection"  only "puromycin selection"  and "antibiotic used as a selectable marker" .  Bottom line is that biology isn't a very regular kind of pursuit. :) Wnt (talk) 02:44, 20 March 2014 (UTC)

Research project ideas for civil engineering
What would be a good research project to write a thesis, for college final year majoring in Civil Engineering which incorporates looking at all parts of an airport rather than just specialised parts of it such as impact loading on runways, materials used on taxiways, geometric design, fire engineering on the terminal structure, materials used for the terminal structure etc. These examples only look at small parts of the airport. Is there anything suitable for civil engineering majors that would involve looking at the entire airport? 82.40.46.182 (talk) 18:46, 19 March 2014 (UTC)


 * If you're interested in the ergonomics of airport design, some airports seem to almost totally ignore the impact on passengers. My local airport, for example (DTW), is an absolute disaster.  Some of the problems:


 * 1) Long-term parking requires taking a bus to the terminals, which involves delays waiting for the bus, waiting for it to let people off at other terminals, etc. (LAX is even worse in this respect, where I got on the bus, then had to wait for the driver to take a dinner break.)  There is often closer short-term parking, but that's absurdly expensive if you need to leave your car there while on vacation.


 * 2) You then often have a long line to check in, then a long line to get through security (which involves removing every bit of metal, and God help you if there's a metal zipper on your pants), then a long walk to the gate, then a long line to get your gate pass. It seems like at least some of those steps could be combined.


 * 3) For some reason, the long walk to the gates at DTW involves going up and down, as the walkway has several dips in it. This can be exhausting, if carrying heavy carry-on luggage.


 * So, I'd redesign the airport from the POV of how to get long-term passengers to their gates in the shortest time. One design might involve a massive underground parking structure in the center for all cars (short-term and long-term) connected by underground tunnels with automated conveyor belts to passenger terminals surrounding it on all sides, and runways around those on all sides, and a ring of cargo terminals beyond those, with fuel depots, warehouses, hangars, and maintenance facilities at the very outside.


 * If you need to take a bus to get from parking to the terminal, that design is a failure, IMHO. You also shouldn't need to go outside from the parking area to get to the terminals.  Rental cars should be picked up and dropped off in the central underground parking area, too.


 * With the current poor airport design, I've found I can drive to Toronto from Detroit in less time (about 4 hours), less expensively, and with less hassle, than I can fly there (although the actual flight takes only 40 minutes). And if you happen to be in a wheelchair, airports are even more of a disaster, so look at wheelchair accessibility, too (keeping everything on the same level helps there). StuRat (talk) 19:14, 19 March 2014 (UTC)


 * How about examining the management of a project to construct a new airport from scratch? Such a project will require a full understanding of all the things you mention, along with the sequencing of their construction, the management of resource delivery, infrastructure, testing procedure, and many others. A particular challenge would be to consider this for a military airfield, where there are very specific requirements that must be met as quickly as possible. Here are a few links you might start with: Military airfield, FAA on Airport Construction, Ledcor construction. Good luck! RomanSpa (talk) 19:30, 19 March 2014 (UTC)


 * For a whole-system approach, I'd think of something involving logistics. Many things need to go in/out of an airport to support a successful flight: e.g baggage, food, fuel, maintenance staff, flight crews, passengers, etc. SemanticMantis (talk) 19:31, 19 March 2014 (UTC)

Things like ergonomics and logistics sound interesting but are they suitable for civil engineering majors? They sound more like something for an architecture major or maybe a management major. 82.40.46.182 (talk) 19:36, 19 March 2014 (UTC)


 * Well, in my design, you could put the control tower directly over the underground parking, and would need to reinforce the parking areas to withstand a terrorist bombing without taking out the control tower. This could involve using arches instead of just cantilever supports, for example.  A redundant external frame design for the control tower is particularly hard to take out.  Does that qualify as civil engineering ? StuRat (talk) 19:45, 19 March 2014 (UTC)


 * I'd argue that a civil engineering student project on airports as whole systems should consider how the infrastructure will support logistics flights. Otherwise, what is the point of all that concrete and steel? SemanticMantis (talk) 13:44, 20 March 2014 (UTC)

The Small Shrink
Given relativity, couldn't we say that we (and all matter in the universe) are shrinking in relation to the observable universe? Just as the observable universe is in theory a "white hole" from the perspective of a black hole.165.212.189.187 (talk) 20:11, 19 March 2014 (UTC)
 * If the universe were shrinking instead of expanding, would distant galaxies still be red-shifted? ←Baseball Bugs What's up, Doc? carrots→ 22:09, 19 March 2014 (UTC)
 * This was making the rounds last year.  I won't try to estimate its plausibility, but maybe someone else will.  Of course, in reality, "there is no spoon" :) Wnt (talk) 22:25, 19 March 2014 (UTC)
 * All kinds of weird stuff makes it onto the arxiv. Physicists have ignored this paper, and probably for good reason.
 * There is cosmological and geological evidence that the microscopic laws of physics that set the size of physical objects haven't changed since the very early universe. I don't have a good source for this but here's one paper that mentions various sources of evidence. It's much easier and seems much more sensible to base length standards on those laws than on a cosmological scale factor. From a philosophical-relativist perspective (heh) I suppose you can go either way, but that doesn't mean that "we're shrinking" is a viable alternative to the standard cosmology—the point of relativism is that it's not a new idea at all, but the same idea described in different words. Special and general relativity have nothing useful to say about this since they're not related to philosophical relativism in anything but name.
 * I don't think the observable universe is a white hole from the perspective of a black hole, either (i.e. I don't think the term "white hole" is normally used that way). -- BenRG (talk) 23:05, 19 March 2014 (UTC)


 * We are used to things flying apart under continued momentum due to an explosion. What is the cause of the shrinking, and why does it continue? Over short distances we notice that bodies do move together, as well as fly apart.  Why don't we notice that bodies grow and shrink in relation to each other?  The space between non-gravitationally bound objects is expanding.  The distance between the sun and the earth is not expanding.  Are the sun and the earth stable in regard to each other, growing in regard to the approaching Andromeda Galaxy, and shrinking in regard to the rest of the universe?  Were the chemical properties of carbon atoms different a billion years ago when they would have been significantly bigger than they are now?  Ockham's Razor μηδείς (talk) 23:04, 19 March 2014 (UTC)
 * I was thinking of a scenario where two distant objects' center points are stationary relative to each other but because they are "shrinking" they only "appear" to be moving apart.165.212.189.187 (talk) 14:23, 20 March 2014 (UTC)


 * There's nothing wrong with playing with such models if you can do the math right. You might want to ask this question again (just copy and paste the whole discussion) at the math desk.μηδείς (talk) 16:50, 20 March 2014 (UTC)

Toothpaste on burns: reality and myth
Does or did it work in some case? Different toothpastes have different ingredients, so, maybe some old toothpastes were good for it, and hence the belief that toothpaste (in general) is good for burns. What if some toothpaste manufacturer decides to change the formula to include something that's really good for the teeth, but really bad for a burn injury? Should they cover this off-label use, even if it's nonsense? OsmanRF34 (talk) 20:51, 19 March 2014 (UTC)
 * There actually could be some beneficial effect. First, it could act as a sort of heat sink (cooling effect) and if it contains actual mint extract (see: menthol) or peppermint (see: WebMD), it would have an analgesic effect.  As to the 2nd part of your question, I checked my toothpaste and there is nothing in that regard (but it did list an 800-number for "questions or comments"). Note: this is not medical advice; just suggestions for finding sources for answers to your query.  ~:71.20.250.51 (talk) 21:24, 19 March 2014 (UTC) [added note:71.20.250.51 (talk) 21:40, 19 March 2014 (UTC)]


 * Almost anything you put on a burn that isn't quantities of cool water, or as close as you can get, is going to be worse than using quantities of cold water, and they'll have to wash it off the damaged skin before they can treat the burn when you get to the hospital. Toothpaste is an abrasive polish: do you really want to be applying an abrasive to an injury? And any cooling effect will quickly be lost when the toothpaste warms to body temperature, which won't take long: that's why you try to run burns under cold running water, if possible: the water would warm up, otherwise.
 * People do terribly stupid things to burns. They think that they should apply butter: butter manufacturers do not require a disclaimer for this, because they have never claimed that this terrible idea was sensible. The disclaimers all end up on first aid materials, telling you that no really, don't do that, just run it under cool water. 86.157.148.65 (talk) 18:35, 20 March 2014 (UTC)
 * Butter's disclaimer: do not use on burns, do not consume too much due to risk of obesity, do not use for anal sex. — Preceding unsigned comment added by 185.13.202.241 (talk) 20:16, 20 March 2014 (UTC)
 * Beans should have disclaimer: "Do not put beans up your nose." — Preceding non-sequitur added by 71.20.250.51 (talk) 20:34, 20 March 2014 (UTC)

Behavioral epigenics
How does changing our behavior alter the expression of a gene that could affect future generations? Maybe before conception? I'm confused as to the effect of our actions shaping the lives of our children, or grandchildren. When should the change occur to make a difference? — Preceding unsigned comment added by 96.24.184.152 (talk) 21:30, 19 March 2014 (UTC)


 * Well, since we are talking about inherited characteristics, it would have to happen before conception, in the case of the father. The mother's behavior might also have an epigenetic impact on the baby during pregnancy.  Starving oneself almost to death would be one behavior that might have an impact.  Of course, you could also starve the child after birth, and thus your behavior could affect the epigenetics that those children then pass down to their children.  StuRat (talk) 21:42, 19 March 2014 (UTC)


 * I was very impressed by . Note however that humans have a much reduced sense of smell and a much less elaborate brain structure to process it, so it is not guaranteed to work the same way there.  Also see .  Those are the two that popped first to mind - for more see behavioral epigenetics. Wnt (talk) 22:21, 19 March 2014 (UTC)


 * Sounds like Lysenkoism to me. --DHeyward (talk) 05:37, 20 March 2014 (UTC)


 * There are elements of lysenkoism in these current theories. What we're homing in on is a system in which the resulting organism is mostly determined by classical Mendelian inheritance laws - have some relatively tiny influence comes from these effects that look a lot like lysenkoism.   It's not a large effect - but it does seem to be there. SteveBaker (talk) 19:19, 21 March 2014 (UTC)

Cutting dead leaves off plants
Should I cut them off while still "juicy" or wait until they are all dried out ? StuRat (talk) 22:23, 19 March 2014 (UTC)


 * If the leaves dry and drop spontaneously from base of the the petiole (botany), you avoid risking damaging the plant by plucking them and taking stem tissue with them or breaking the stem accidentally. If the leaves do not drop by themselves, or if they are diseased cut them off as close t the petiole without damaging the stem as possible.  So yes, let them dry, unless there's some good reason otherwise. μηδείς (talk) 22:50, 19 March 2014 (UTC)


 * Here's a better image of the base of a leaf. If you must cut, avoid cutting the stipule or the axillary bud.  But the best way is to wait until the leaf falls of its own accord with a slight breeze or touch. μηδείς (talk) 22:58, 19 March 2014 (UTC)


 * If I wait until it's dried out, then I can cut off all of dried part, right? StuRat (talk) 23:15, 19 March 2014 (UTC)


 * (EC, basically agreeing with Medeis above) This can vary by plant. In general, wait until they are dried out. nitrogen translocation or retranslocation come into play, and let the plant 'recycle' nutrients by moving nitrogen and other useful compounds into storage organs, that can later be used to make new leaves. (both of those are surprising redlinks, best I can find on WP is a terse statement at the disambig for translocation... see e.g. for the idea). A classic example of people doing it wrong: when people plant bulbs like narcissus or hyacinth, they often cut off the greens before they are brown, because they are considered inaesthetic. However, that's the worst thing to do, and deprives the plants of resources, and will result it poor plant performance the next year.


 * There are also considerations as to why leaves are dying. If it's seasonal die-off, then absolutely leave them. Entering seasonal dormancy for an outdoor plant is unlikely in the USA this time of year. If it's a disease of some sort (indicated by patterned or spotted browning on leaves), then remove leaves as soon as possible, to prevent further sources of infectious agents. If you want more specific advice, I could do much better with at least the family_(biology) of the plant, a photo, or even a description (e.g. indoor or outdoor, woody or herbaceous, in pot or in ground, etc.) SemanticMantis (talk) 22:59, 19 March 2014 (UTC)


 * Agreed it's strange the redlinks we have on plant biology. I can't even find a good image of the parts of a leaf.  Stu should understand the importance of nutrient reabsorption in general, but also be reassured that once the leaf is full dry there will be no more transport.


 * The lower leaves on this particular plant seem to naturally die off as it grows taller. StuRat (talk) 23:11, 19 March 2014 (UTC)


 * A picture really would be best, can you upload one? If it is just old leaves and not actual stem that is dying you should avoid cutting.  If the main stem is dying, let us know.  In most plants, old senesced leaves will simply fall by themselves when ready will simply pop off at the pulvinus (the little bulb like you find at the end of elm and oak petioles) if you touch them lightly or blow on them.  You should never have to apply enough force to pluck them, as this may cause green stem to snap and tear away tissue below the stipule (see the picture I linked to).


 * An exception will be monocots like grasses and lilies where the leaf often wraps around the base of the stem. These too should always be let stand unless they are dying of a pest or fungus (in which case, you have to amputate). Once they are dry remove gently at the base with knife or scissors as necessary always avoiding damaging the stem.  The big hint is "do no harm". μηδείς (talk) 23:54, 19 March 2014 (UTC)


 * I guess this is some type of a vine, as it keeps growing upwards yet can't support it's own weight. (I've transplanted a part that broke off, and am now supporting the 2 stalks as best I can.) StuRat (talk) 00:00, 20 March 2014 (UTC)


 * "Vine" is a shape, like tree or herb, not a family of closely related plants. It could be anything from Spanish Moss to English Ivy to various jade plant relatives.  Ivies generally have one long, week growing axis, with leaves on one side, and adventitious roots at the basis of the leaves.  You may simply have a sun-loving plant that needs direct sun and pruning to encourage it to branch out, rather than keep growing in one direction as if searching for the One Ring. μηδείς (talk) 00:20, 20 March 2014 (UTC)