what ww u got ? what type of light u use and mostly , whats the excact distance of the top colas from the light source , if u use hid's close to the plant is normal to delay the top formation while the lower branches enjoy lower temps and as mention above , CHECK THE TRICHS , do u have a camera with macro ability ? a good magnyfuing lens ( 2 or three in a row do the tricjk better ) , even binoculars reversed can tell u the truth