Cannabis Male & Female plants
Cannabis is a dioecious plant, which means male and female flowers develop on seperate plants. Female plants are commonly referred to as pistillate (having pistils) and male plants staminate (having stamens). For good quality marijuana we are only interested in the female plants. Sometimes monoecious examples with both sexes on the same plant are found, and these are commonly known as hermaphrodites. Unless needed for breeding purposes, any staminate plants (males) should be removed at the first sign of sex. If the males are left to shed their pollen, any pistillate plants (females) in the same area will be fertilised and produce seed. Once a female plant has been fertilised she turns all her energy into producing seed, and much less energy producing T.H.C. After a few weeks, the seed has matured and the plant dies having completed it's life-cycle.
By removing male plants before fertilisation has occured a grower is able to manipulate females into flowering much longer, all the while increasing T.H.C production. This is known as the art of growing sinsemilla or seedless marijuana.
Feminized seeds / Female cannabis seeds
Growing Marijuana is not the most difficult thing to do, it is a weed that will grow almost everywhere. The Yield will depend on many circumstances and on the fact they don't get fertilized.
Fertilized females will grow smaller buds because she will put all her energy in making new seeds for next year. If you don't know the difference between a male or a female plant, or you don't have the time to check them everyday, it could be wiser to get feminized seeds so you are sure that you only get female cannabis plants. A male marijuana plant can destroy most of your yield and you end up with lots of seeds but (almost) nothing to smoke and that is bad.