Question about temperatures?

I have read on here that the temps need to be in the 70's for proper growth, and I was wondering how people come up with that? I am just trying to clarify in my mind how this came to be the general conscientious so if someone can explain it to me I would appreciate it. I can see how breeds such as Northern Lights that were designed to grow in the North would require low temps, but I do not see how this would hold true to all varieties (just tell those boys down in Mexico that you can't grow weed in 95 plus heat with high humidity). Isn't the day/night split equally important? Anyway, if someone could help me understand this it would be awesome.

I've been wondering about that a little bit myself. CO2 seems to require 85-95*F, while earth atmosphere is supposed to be kept at 70-80. I've heard that the plants won't grow above 85, but much of the world is above 85*, and growth is anything but an issue.

My temps stay between 75 to 80 during the day, and at night 65 to 70*F.

Light is easy. Marijuana knows when to seed according to the day length. 12 hours+ of darkness= flowers.

There is a chemical (hormone?) in marijuana that is destroyed in the presence of light. I can't recall the name of the chemical (hormone?) . When the chemical is present in the plant for less than 12 hours per day, it will remain in vegatative growth indefinitely.

Yes, I read that article as well on the light/night 18/6- 12/12 hormone changes and my girls are on the 12/12 cycle. I can not get my temps to go lower than 82 with the lights on but my growth rate is just fine. I do know they need a temperature split from night too day and I get around a 10 degree split. The temp thing is just something that has been bothering me so I thought I would just kind of toss it out to see what others had to say.

Depends how you're growing. If you're pure organic with live predators involved, temps become much more important.

Optimum temp is around the mid 70's and a plant starts to slow down above 85, or below 60. I have grown with temps in the low 90's. Plants don't like it, but they do survive. I try to maintain 80-85 at the canopy, which in a small area with HID lights is about as good as it gets