Which part of the poppy plant is used to obtain the drug "Smack"?

The latex of the poppy plant Papaver somniferum is used to obtain heroin, which is commonly known as 'Smack'. It is a white crystalline, odourless, bitter compound which is chemically called diacetylmorphine (it is formed due to the acetylation of morphine). It acts as a depressant and slows down action of the nervous system.