I'll post this again for your multi-post I posted in the newbie section with your same question.-----
When Cannabis is grown for sinsemilla floral production, the cycle is interrupted. Pistillate plants remain unfertilized and begin to produce capitate -stalked trichomes and accumulate resins in a last effort to remain viable. Since capitate- stalked trichomes now predominate, resin and THC production increase. The elevated resin heads appear clear, since fresh resin is still being secreted, often being produced in the cellular head of the trichome. At this time THC acid production is at a peak and CBD acid levels remain stable as the molecules are rapidly converted to THC acids, THC acid synthesis has not been active long enough for a high level of CBN acid to build up from the degradation of THC acid by light and heat. Terpene production is also nearing a peak and the floral clusters are beautifully aromatic. Many cultivators prefer to pick some of their strains during this stage in order to produce marijuana with a clear, cerebral, psychoactive effect. It is believed that, in peak floral clusters, the low levels of CBD and CBN allow the high level of THC to act without their sedative effects. Also, little polymerization of resins has occurred, so aromas and tastes are often less resinous and tar like than at later stages. Many strains, if they are harvested in the peak floral stage, lack the completely developed aroma, taste and psychoactive level that appear after curing. Cultivators wait longer for the resins to mature if a different taste and psychoactive effect is desired.
This is the point of optimum harvest for some strains, since most additional calyx growth has ceased. However, a subsequent flush of new calyx growth may occur and the plant continue ripening into the late floral stage.(marijuana botany)