For my 2 cents...
My preference is for 24 hours a day for veg, and then I shift right to 12/12 for flowering. I always veg for less than 3 months before flowering.
I tried 18/6 for several crops and went back to 24 hours. IMO, they grow faster under constant light.
I did not notice any difference in the male/female ratio between the two light schedules.

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What this supposed to mean? The male gene is always present just to a lesser degree? You mean sometimes it pops up but most of the time it doesnt? You'll have to forgive me for not buying into this in any way shape or form.

A female plant does NOT carry male genes, either in its genetic form or its hermaphrodite form. As I said earlier -

" One pair of chromosomes carries the primary genes that determine sex. These chromosomes are labelled either X or Y. Male plants have an XY pair of sex chromosomes. Females have XX. Each parent contribute one set of 10 chromosomes, which includes one sex chromosome, to the embryo. The sex chromosome carried by the female ovule can only be X. The one carried by pollen of the male plant may be either X or Y. From the pollen, the embryo has a 50/50 chance of receiving an X, likewise for Y; hance, male and female progeny appear in equal numbers (in humans, the sperm carries either an X or a Y chromosome.)"

I'm afraid the female plant with the XX chromosomes, doesn't suddenly change to XY just because it turns hermaphrodite I'm afraid - they remain XX.

Feminised seeds do NOT produce male plants, they produce either female or genetic hermaphrodites. If they do (and you've witnessed it) please demonstrate it to me. Out of all the grows using feminised seeds on this site you won't find one single seed has produced a male plant. That's not 'not as dominant as the female gene'.

Skunkushybrid is intelligent enough to figure things like this out for himself.

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Originally Posted by babygro
Environmental Effects
If artificial light is used, the length of the photoperiod can influence sexual expression. Normal flowering, with about equal numbers of male and female plants, seems to occur when the photoperiod is from 15 to 17 hours of light for a period of three to five months. The photoperiod is then shortened to 12 hours to induce flowering. With longer photoperiods, from 18 to 24 hours a day, the ratio of males to females changes, depending on whether flowering is induced earlier or later in the plant's life. When the plants are grown with long photoperiods for six months or more, usually there are at least 10 percent more male then female plants. When flowering is induced within three months of age, more females develop. Actually, the "extra" males or females are reversed plants, but the reversals occur before the plants flower in their natural genders.

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I believe that you posted the second study that I was talking about (see above).

This seconds study seems to indicate that a shorter veg. stage helps produce more females. I assume that by using 24/7 and MH lights will quicken the veg. stage more than using 18/6 and other types of lights?

The first study that this thread is based on states that more darkness or less light (18/6) during the veg. stage will product more females. This will length the veg. stage somewhat. There is the difference in the 2 studies.

By the way, do you have a science or technical background? You seem to be a lot more analytical than myself. In otherwords, people on this forum should go by what you say more than myself. I am just a newbie that what to learn and pass onto others when possible. Thank you.

This is all well and good... except cannabis plants do not share the same XX/XY chromosome system that mammals do. Your argument is based on a faulty assumption.

Some credible research is here: http://links.jstor.org/sici?sici=000...R%3E2.0.CO;2-7

It really isn't disputable that some plants' gender can be influenced by environmental factors. It appears that this is the case with marijuana as well. I'm a little skeptical that what Dutch Passion is completely factual, but it definitely is not completely unreasonable.

FWIW, I immediately assumed that this was a load of crap... but the more you look into it the more it makes sense.

So it's not unreasonable that Dutch Passion have discovered a way to get 90% females from normal seed?

I'm trying to stay out of this now as I have explained enough. If this is not clear to others then I'm happy for them to prove me wrong.

Dutch Passion were on about getting a 90% ratio from hermied plants... not natural hermies... but forced hermies. A hermie seed from a forced hermie is a natural hermie, and should have 100% fems and hermies.

From a forced hermie, I imagine sex wise that the seeds (and eventual plants) would be quite volatile, and much more responsive to environmental factors.

In fact even seed from a natural hermie have certain stability factors, so that a fem can be easier turned into a hermie than a fem from normal seed.

I mean this is bad information. A guy on this site took it to heart and told people in a thread that beginner growers should expect 90% males... with, as you progress and learn more, better results in the fem/male ratio. Total bullshit.

It seems like videoman has just come back to be disruptive, I cant believe either that you can guarantee sex by following any guidlines, the only way to make sure that you get a female ratio of 80% or higher is to buy fem seeds.

I dont get it, if a seeds sex is already decided, and this is what most people seem to agree on, I dont see how it can completely reverse its sex later on, I can understand it becoming hermie but a complete sex reversal seems to be untrue, if this was the case it would be in all grow guides and everyone would be doing it and there wouldnt be a need for fem seeds.

If dutch passion really had found a way of reversing sex without using chemicals and creating hermies, I'm sure that this secret would be closely guarded.

I don't think VM's being disruptive... we need to argue these points so that we can learn. I'm not arguing for the sake of it, i honestly believe I am right. I know VM thinks he is right too, yet we are at an empasse.

Dutch Passion haven't helped much with their wording, and I have in fact noticed this info' on cannabis information sites, word for word obviously stolen/cut n pasted from the DP website. This info is wrong, and it seems to be spreading. It seems the only people capable of shedding light on the subject are DP themselves.

Anyone got any ideas?

The thing is, sex isn't completely already decided. There is no accepted way of modeling sexual expression in cannabis plants.

From wikipedia:
Dioecy is relatively uncommon in the plant kingdom, and a very low percentage of dioecious plant species have been determined to use the XY system. In most cases where the XY system is found it is believed to have evolved recently and independently. Since the 1920s, a number of sex determination models have been proposed for Cannabis. Ainsworth describes sex determination in the genus as using "an X/autosome dosage-type."
[...]
Many researchers have suggested that sex in Cannabis is determined or strongly influenced by environmental factors.
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I agree with your last post, skunk, but the idea of increasing your female to male ratio through environmental factors has some validity. It is probably a good idea to follow the guidelines set by DP (hehe, DP), but I wouldn't expect to reach any of the outrageous claims.

My friend, a biology major, told me that there are examples of complete gender reversal from environmental factors in some animals. It doesn't make a lot of intuitive sense, but it's not unprecedented.

I'd love to argue this point with you babygro, but as I read the thread again, I see that you still believe roots only grow at night too, another myth.
Seeing as where you are coming from, I'm not going to dive into this with you, as you've also put me in a position of doing what, producing a plant that was obviously killed months ago?

Do some reading, or post the question in one of the other forums you frequent.

Female seeds to give a much high ration of females, but hermies are possible and so are males. It is not a guaranteed, magical answer to always get only females.
Peace

all untrue hermies will produce males. If you hermie one of your plants, the seed from it will be very, very unstable no matter what sex it is. Even seed from a natural hermie are unstable.

Roots only grow in the dark, not at night. It should always be dark/night to your roots. They shy away from the light. I have witnessed this myself by growing a plant/runt in a clear plastic tub.