Cultivation has produced grades intermediate between these varieties sometimes difficult to distinguish. The capsules of the poppy, or poppy-heads should always be gathered before they have ripened, at this time they abound in the juice from which opium is formed, and which becomes greatly diminished when the capsule has fully matured. When dried, the unripe capsules possess the peculiar bitterness and narcotic qualities of opium, which are hardly observable in those that are allowed to ripen. The capsules of the white poppy are larger than those of the black . They owe their virtues entirely to the opium contained in them.
Some varieties have the lower end narrowed and prolonged.
Where the fruit joins the stalk there is a tumid ring. The stigmas are peltate and sessile, from 8 to 20 in number, constituting sharp, angular ridges agreeing in number with the carpels. The placentae are also of the same number, projecting into the 1-celled interior so as to form incomplete partitions. On their faces and edges are borne the minute kidney-shaped seeds in immense numbers. Sacc, in 1849, obtained about 55 per cent of oil from the seeds, with 23 per cent of mucilage and 12.6 per cent of protein matter.