The leaves of all the "Tilia" species are heart-shaped, and most are asymmetrical. The tiny, pea-like fruit hangs attached to a ribbon-like, greenish-yellow bract whose apparent purpose is to launch the ripened seed clusters just a little beyond the parent tree. The flowers of the European and American "Tilia" species are similar, except the American ones bear a petal-like scale among their stamens and the European varieties are devoid of these appendages. All of the "Tilia" species may be propagated by cuttings and grafting, as well as by seed. They grow rapidly in rich soil, but are subject to the attack of many insects. "Tilia" is notoriously difficult to propagate from seed unless collected fresh in fall. If allowed to dry, the seeds go into a deep dormancy and take 18 months to germinate.