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Toshikazu Matsumoto, Yoji Nako, Chiaki Takahashi, and Akira Sakai

We thank Dr. T. Niki, Associate Professor, Takushoku Univ., Tokyo, for his valuable advise on the method of histological observation for thin sections. We also thank Dr. B. Leckett, Quanta Vision, Canada, and Mr. J. Lawn, Macquarie Univ

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A.R. Kuehnle and N. Sugii

the Hawaiian Anthurium Industry Assn. We thank D.G. Fisher for histological advice. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked

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Rebecca M. Cade, Todd C. Wehner, and Frank A. Blazich

Two studies were conducted to test the effects of various tissue culture media on somatic embryogenesis from cotyledon tissue of cucumber (Cucumis sativus L.). The two best media for embryo initiation were Murashige and Skoog (MS) salts and vitamins containing either 1 or 2 mg 2,4-D/liter and 0.5 mg kinetin/liter. In the second study, embryos developed more normally. More plantlets developed when tissue was removed from the initiation medium after 3 weeks and transferred to MS containing 1 mg NAA/liter and 0.5 mg kinetin/liter for 3 weeks, rather than leaving the embryos on a medium containing 2,4-D. Histological evidence indicated that the embryos were multicellular in origin. Charcoal in the maturation medium inhibited embryo development. Chemical names used: (2,4-dichlorophenoxy) -acetic acid (2,4-D); N-(2-furanylmethyl)-lH-purine-6-amine (kinetin); 1-naphthaleneacetic acid (NAA).

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Richard K. Schoellhorn, James E. Barrett, Carolyn A. Bartuska, and Terril Nell

Effects of heat stress on viable and nonviable axillary meristem development and subsequent lateral branching in 'Improved Mefo' chrysanthemum [Dendranthema ×grandiflorum Ramat. (Kitamura)] were studied. Plants grown at 33 °C day/27 °C night produced more nonviable buds than did plants grown at 23 °C day/18 °C night. A negative linear relationship {y = 28.7 + [-0.66 (x days)], r 2 = 0.70} between timing of exposure to high temperatures and the number of nonviable buds was observed. Histological examination 28 days after exposure to 33 °C/27 °C revealed that plants showed both normal and abnormal bud development. Abnormal bud development occurred as a consequence of premature differentiation of axillary meristematic tissue into nonmeristematic parenchyma tissue immediately after separation of axillary from apical meristems.

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Chamchuree Sotthikul and Pimchai Apavatjrut

Propagation of Curcuma roscoeana in vitro was done successfully by culturing 0.5 × 1.0 mm shoot tips from young buds onto modified MS (1962) + 0.25 mg·L–1 kinetin. The bud-derived new plantlets could be multiplied on a new medium. Stem explants 10 mm in size, measured from base of the plantlets longitudinally cut in half, were the most suitable culture explants providing 2.8 new healthy plantlets/cultured explant. Explants from 4, 6, and 8 weeks old plantlets were more suitable than those of 2 weeks old when grown on agar or in liquid medium. From a histological study, it was found that new buds developed from preexisting meristems. The buds, like root initiation, could also occur directly from initial culture explants, not through callus. The plantlets obtained could successfully be transferred into growing pots, having a 95% survival rate.

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Janet S. Mrosek and Stephen C. Myers

The relationship between cell division, nonstructural carbohydrates and fruit size was investigated using 5-year-old `Encore' peach [Prunus persica (L.) Batsch]. The trees, which were trained to two opposing scaffolds, were selected for uniformity based on tree size and floral bud density. One-year-old shoots ranging in size from 20 to 30 cm were tagged from throughout the canopy. At anthesis, one entire scaffold was thinned of 75% of its flowers, leaving 25% in the mid-section of each shoot. The opposing scaffold served as the control. Samples were taken at three intervals for histological analysis: Anthesis, 30 days, and 45 days after full bloom. Nonstructural carbohydrates were analyzed on samples taken at five intervals: Anthesis, 10, 20, 30, and 45 days after full bloom. Volumetric size increased 29% by 30 days after full bloom, and 64% by 45 days after full bloom. Final fruit size (volumetric) was increased 8% by harvest.

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Sharon Bates, John E. Preece, John YOPP, and Robert Trigiano

Dissected white ash seeds were placed on a MS basal medium containing 10 μM TDZ and 1 μM 2,4-D. Adventitious buds formed directly and indirectly on cotyledons and hypocotyls that were in contact with the medium. Histological observations after 7 days from initiation indicated early divisional events originated directly in subepidermal layers on adaxial portions of the cotyledons. As these cells divided, the growth ruptured the epidermis. Bud-like structures were seen at 3 weeks. After transfer to a secondary medium containing 3 μM TDZ, 1 μM BA, and 1 μM IBA, some of adventitious buds elongated. Efforts (gibberellin, etiolation, ABA, and silver nitrate treatments) to increase the number of elongated buds have been unsuccessful. Excised adventitious shoots were rooted under mist and established in the greenhouse.

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K.R. Malueg, S.E. Schlarbaum, E.T. Graham, and R.N. Trigiano

Development of Cornus florida L. pollen was monitored using standard paraffin histological techniques and light microscopy. Terminal buds (putative floral buds) were collected over a 6 weeks from mature landscape trees located on The Univ. of Tennessee Agricultural Campus, Knoxville. Examination of samples taken at 3- to 7-day intervals revealed variations in development representing 1- to 2-week differences between florets in a single inflorescence, florets on the same tree, and florets from different trees. Floral initiation occurred before 19 July in the 2 years of this study. Pollen development followed typical angiosperm stages: tapetal cells were multinucleate, pollen tetrads were tetrahedral, and meiosis occurred late in the developmental period. Pollen grains appeared morphologically mature by early September in both years.

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Carl E. Motsenbocker, Marshall D. Sundberg, and Yuehe Huang

Two lines of tabasco pepper (Capsicum frutescens) were previously identified that differ significantly in ease of fruit detachment force. Greenhouse-grown plants of these lines, `McIlhenny Select' and `HP', were investigated for differences in cell organization in the fruit-receptacle area and the separation zone at different developmental stages. Histological examination indicated that fruit of `HP', which requires greater force to separate, exhibited a larger region of sclerified cells within the fruit-receptacle area. In contrast, fruit of `McIlhenny Select', the line that detaches easier, had fewer sclerified cells in this region. Cell sclerification increased for both lines with increasing fruit maturity. The fruit-pedicel separation zone in both lines is distal to the sclerified region and is composed of parenchymatous fruit tissue. The separation zone for `HP' includes at least 10 additional distal cell layers in the fruit septal region than `McIlhenny Select'.

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Maryke A. Cleland, Cynthia Jones, and Mark H. Brand

An interspecific hybridization program involving five species of Impatiens was initiated to delineate incompatibility barriers. With the exception of one cross, no viable hybrid seed was recovered. Fluorescence microscopy revealed foreign pollen tubes to reach ovules in all crosses, although not all ovules were approached. A histological study involving I. auricoma Baill. and I. walleriana Hook f. ensued to confirm the presence of hybrid embryos. Developing I. walleriana × I. auricoma and reciprocal hybrid embryos were compared to self embryos. Development of hybrid embryos was delayed as early as five days post-pollination. I. walleriana × I. auricoma embryos continued to develop for 8 days post-pollination, but did not reach a size greater than a 5-day self embryo. Excessive endosperm was observed in the hybrid. I. auricoma × I. walleriana embryos continued to enlarge up to ovary abortion but did not reach a size greater than a 7-day self embryo and little to no endosperm developed. Disintegration of ovules included disorganization and collapse of the endosperm, and vacuolization and loss of turgidity of the embryo.