In the beginning, most roses had single flowers, composed of five petals. Obviously, rose blossoms now usually far exceed five petals. Roses with nine to 16 petals fall into the semi-double class. Seventeen to 25 petals on a rose denotes a double flower. Full is the designation for a flower with 26 to 40 petals, and very full refers to any rose featuring over 40, up to 150, petals. Actually, these roses still only possess five true petals. The remaining petaloids are modified stamens, producers of the flower's male pollen. This means that very full rose blooms probably have few to no functional stamens, making them sterile as male parents. Since such plants seldom perpetuate themselves in nature, rosarians must cultivate them in the laboratory.