The first preflowers usually form near the middle of the plant then sporadically in other places , the older a plant gets the more preflowers it will have. The will usually show there first preflowers right around the time the nodes (branches) start alternating instead of forming in pairs. You will be able to spot them at the "v" where the branch splits off, at first they all look the same (like a lil numb)so dont kill a plant until your sure its a male. A female preflower will look sort like a tear drop with a pointy end and grow 1 or 2 little white hair's comming out of it , while a male will look more like a "ball on a stick" and male preflowers will form in little groups or clumps of pre-flowers (you will see male preflowers form more then one next to each other ;first there will be one then more will grow next to it) Dont kill a plant until you see sets of "balls" growing lol. Thanks for your complements on my grow.