ANATOMICAL AND PHYSIOLOGICAL STUDIES OF FLORAL TUBE ELONGATION OF CROCUS VERNUS (IRIDACEAE)

Intact floral tubes of Crocus vernus grown under controlled conditions elongated 50 mm in 8 days. Mitoses of the epidermal cells did not occur during the growth of the intact tube; however, cells did elongate from 50 gm to 150 gm, a three-fold increase in cell length. When the floral buds were excised and maintained in distilled water, elongation of floral tubes was inhibited by 46%. The presence of the ovary or the addition of nutrients had no significant effect upon the elongation of the floral tubes of excised buds. When the excised floral buds were placed in l0-6 M indoleacetic acid, the final tube lengths exceeded that of the water controls by 30% and achieved 91% of the elongation of the intact tubes. Gibberellic acid and kinetin had no effect on floral tube elongation. As with the intact floral tubes, mitoses of the epidermal cells did not occur during the elongation of the excised floral tubes. CROCUS, A SPRING FLOWERING ORNAMENTAL PLANT of the family Iridaceae, is a typical cormose plant. Flowers and leaves are initiated in the fall, and growth is suspended until a cold treatment has taken place. In very early spring, the leaves and flowers undergo extensive elongation. However, nothing is known about the relative contributions of cell division and elongation during the formation of the large showy purple flowers from small floral buds. After the flowers wither, new corms are produced asexually above the old corm which eventually shrivels. If a young corm is formed near the soil surface, fleshy contractile roots will pull the corm into the soil (Rockwell and Grayson, 1977). Physiological studies of the saffron crocus (Crocus sativus) revealed that treatment of dry corms with gibberellin and kinetin reduced the time required for the transition from vegetative growth to generative development (Azizbekova, et al., 1978). Leaf and root length increased, and additional floral buds were initiated from undifferentiated primordia. A further anatomical investigation of Crocus sativus described the transformation of vegetative apices into floral apices (Milyaeva and Azizbekova, 1978). Other anatomical studies of floral tube formation within the Solanaceae have described the fusion of floral parts to form the corolla tube (Daniel and Sattler, 1978; Nishino, ' Received for publication 18 July 1981; revision accepted 11 March 1982. This study was sponsored by the Watkins Scholarship Program at the University of Montana and could not have been accomplished without the direction and encouragement of Dr. David Bilderback and the invaluable support of the Botany Department. 1978). However, floral tube elongation has not been investigated in any previous studies. MATERIALS AND METHODS-Corms of Crocus vernus Wulfen (Bailey, 1949) were purchased from the George W. Park Company, Greenwood, S.C. The giant-flowered, earlyblooming Dutch varieties, Paulus Potter and Striped Beauty, were selected for flower size and ease in induction of floral development. Six corms were planted 7 cm deep in a soil mixture of equal parts peat, loam, and vermiculite in 15-cm plastic pots. The pots were watered thoroughly and placed in a cold-room at 0-10 C in constant darkness to insure adequate root growth and floral development. The plants were examined every 2 wks and watered from below when the soil became dry. After 8-10 wks, roots appeared through the drain holes of the pots, and the embryonic leaves with surrounding bracts extended approximately 3 cm above the soil surface. The pots were then transferred to a growth chamber with a 12-hr photoperiod and a constant temperature of 12.5 C. The radiant density of the growth chamber was 10 watts/M2. To measure the growth of intact floral tubes, the enclosing bracts were removed, and the tubes were marked at 2-mm intervals with India ink (Fig. 1). The distance between the marks was observed daily for eight days. Floral buds were removed from the plant below the ovary and trimmed to the base of the ovary (Fig. 2). After the pedicel was removed, the buds were measured and inserted through individual holes in a plastic lid on a 120-ml culture jar containing the appropriate solution. Each culture jar held five floral buds,