Lewisia tweedyi (A. Gray) Robinson is an endangered, herbaceous perennial native to the Cascade Mountains of northern Washington state and southern British Columbia. It is highly valued as an ornamental, but has a reputation for being challenging to grow and is only cultivated by alpine specialists. The better known Lewisia species, L. cotyledon, is a minor commercial crop in some areas of Europe and western North America. Lewisias are members of the Centrospermae; a linear peripheral embryo surrounds centrally located perisperm. Lewisia tweedyi seed is distinct from all other lewisias in having a fleshy appendage, or caruncle. Germination practices include stratification for an unspecified period in a garden cold frame. In addition to a long germination period, percent germination is characteristically low. A number of tests, including sowing under axenic conditions, and combinations of prechill periods and liquid N scarification were conducted. Seedcoat-imposed dormancy and germination requirements have been determined.
Christia M. Roberts
Naza Azizbekova, Christia M. Roberts, Stefanie Butland, and Brian Ellis
Scilla peruviana is a bulbous plant whose distribution extends from South Africa, into Europe and Asia. It belongs to the family Liliaceae (subclass Monocotyledonae). S. peruviana is an attractive floral species with excellent commercial potential, but it does not produce many bulblets and its multiplication rate is very low. Increasing the multiplication rate, and regulation of its growth and development, cannot be achieved without knowledge of its basic patterns of ontogenesis. We studied the annual growth and development of S. peruviana, from initiation until differentiation, giving special attention to cytological changes at the apical meristem. We also investigated the cytophysiological changes occurring in scales during ontogenesis. Two generations of daughter bulbs are present in each mother bulb. Flowering of the mother bulb coincides with vegetative development of the apical meristem of the primary daughter bulb (March-April). During gradual senescence of leaves and roots of the mother bulb, the apical meristem of the primary daughter bulb undergoes a transition from vegetative to prefloral development (June). Intensive flower organ differentiation occurs in the daughter bulb during the mother bulb's rest period (July–August). Initiation of the apical meristem of the secondary daughter bulb occurs within the primary daughter bulb, which is itself enclosed within the mother bulb (August). The development of the apical meristem of a daughter bulb, from its initiation until flowering, thus occurs without interruption and takes ≈20 months. By modifying external factors such as temperature and growth regulators, we can now control time of flowering and increase the multiplication rate of S. peruviana.
Naza Sh. Azizbekova, Stefanie L. Butland, Brian E. Ellis, and Christia M. Roberts
The growth cycle of Scilla peruviana L. involved the development of two generations of daughter bulbs enclosed within each mother bulb. Flower initiation of the primary daughter bulb took place in June as the mother bulb apparently entered dormancy. Floral differentiation was complete by late October, by which time the apical meristem of the secondary daughter bulb had developed for 3 months inside the primary daughter bulb. The complete cycle of ontogenesis, from meristem initiation to flowering, occurred without interruption and required 20 months. Small zones of meristematic cells detected at the bases of bulb scales may be the origin of adventitious bulblets in this species. This detailed cytological study enabled the development of an effective commercial forcing program for S. peruviana.