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K.R. Maluea, R.W Holton, S.E. Schlarbaum, E.T. Graham, and R.N. Triaiano

Cornus florida L. floral development was monitored using standard paraffin histological techniques and light microscopy. Terminal buds (putative floral buds) were collected over 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 July 19th in the 2 years of this study. Floral development followed typical angiosperm stages. Florets, although small, appeared morphologically mature by early September in both years.

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Kathleen M. Bourke and Robert E. Lyons

Gaillardia pulchella is an annual wildflower with ornamental potential native to the South and Southern West part of the U. S. This experiment attempted to further describe the long day (LD) flowering requirement, approximate the length of the juvenility phase, and characterize apical events during floral initiation. Plants were transferred from short day to LD at various leaf numbers and the time to first flower was recorded from the onset of LD. A quadratic response described the data and indicated that a minimum of 19-20 expanded leaves were needed to flower most rapidly (49 days) once placed in LD. Histological results characterizing apical events will also be discussed.

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Allen D. Owings and Steven E. Newman

The action of foliar-applied uniconazole, paclobutrazol, dikegulac-sodium, ancymidol, 6-BA, GA4+7, and 6-BA + GA4+7 On container–grown Photinia × fraseri was studied over a one year period. Vegetative growth habit was evaluated at three month intervals. Shoot dry weight and histological examination of stern anatomy in the apical meristematic region was conducted at experiment termination.

Several plant growth regulators, primarily uniconazole, 6-BA, 6-BA + GA4+7, and dikegulac-sodium, stimulated lateral branching. Linear increases in lateral branching occurred as application rates increased. High application rates of uniconazole and paclobutrazol created an asymmetrical growth habit and decreased dry weight accumulation.

Open access

H. C. De Roo

Abstract

The water economy of plants often is seriously unbalanced by root destruction or vascular occlusion induced by various rot organisms. Water absorption by the roots and water transport within the plants is impeded and wilting follows. Beckman (1) reviewed the literature on the histological and physiological changes in host plants infected with pathological wilts. Dimond and Edgington (2), studying the mechanics of water transport in healthy and Fusarium-vrilted tomato plants, pointed out the tremendous pressure deficits that are required to maintain normal water flow into leaves through partially plugged vessels.

Open access

Daniel C. W. Brown

Abstract

More than 1000 higher plant species have been reported to regenerate in vitro via either somatic embryo formation or shoot formation (1, 9, 11, 12, 16, 27, 40, 42, 45, 46). Although many reports of plant regeneration are not accompanied by the necessary developmental or histological evidence for verification, it is apparent that most successes follow an organogenic rather than an embryogenic route. However, regardless of which developmental pathway is followed or the complexity of the protocol that is used ultimately to recover a complete plant, much of the work on in vitro regeneration can be described as empirical in nature.

Open access

Yong-Hwan Kim and Jules Janick

Abstract

Somatic embryos were induced from the primary callus of celery (Apium graveolens L. cv. Utah Improved #15) arising from leaf blade explants placed on Murashige and Skoog (MS) salts and vitamins medium supplemented with 9 μM 2,4-D for 4 weeks and then subcultured to 2,4-D-free MS medium. The histological origin of somatic embryos was from single cells along the surface of callus clumps. Embryos proceeded in a standard developmental pattern through the globular-, heart-, and torpedo-shaped stages. Secondary somatic embryos occurred on the cotyledons and hypocotyls of primary embryos. Chemical names used: 2,4-dichlorophenoxyacetic acid (2,4-D).

Open access

G. L. Fuller and A. C. Leopold

Abstract

Ovary stimulation in cucumber (Cucumis sativus L. cv. Crusader) is accomplished rapidly after pollination. Increases in fruit growth are measurable within 24 hours. Experiments where styles were severed from ovaries at intervals after pollination indicate that the signal for ovary growth is received 12-18 hours after pollination. Histological examinations showed that at 12 hours pollen tubes have just penetrated beyond the base of the style into the ovary. Pollen tubes penetrated ovular tissue to accomplish fertilization 30-36 hours after pollination. This timing indicates that cucumber fruit-set is regulated by interactions between pollen tubes and pistillate tissue prior to syngamy.

Open access

Griffith J. Buck and Bunny J. Heppel

Abstract

A study of the histology of the bud-graft unions involving a rose cultivar, Rosa × ‘Fire King’ and two rose understocks, R. multiflora, ‘Brooks’ and R. × ‘Manetti’, was made. These 2 combinations produce a growth phenomenon termed “brittleness”. The graft unions were characterized by large quantities of fragments of necrotic material in the understock-scion interface and delay in the reconstruction of the cambial cylinder with a corresponding decrease in thickness of the cylinders of cambial derivatives derived as a result of cambial activity.

Open access

D. A. Eggert and R. A. Hayden

Abstract

Severe symptom of internal bark necrosis (IBN) were noted when trees of ‘Red Delicious’ (‘Bisbee’ strain) on the EM II rootstock were grown hydroponically for 5 months in a complete nutrient regime supplemented with 50 ppm Mn. Lower levels of Mn resulted in less severe symptoms. Experimentally induced lesions were histologically identical to those occurring naturally in the field. Upon histochemical testing, frozen tissue sections obtained from trees grown in excess Mn regimes revealed localized and heavy accumulation of Mn in both incipient and well developed lesions. Localized accumulation of excess Mn may directly cause cell death and lesion formation.

Open access

L. H. Aung, H. H. Bryan, and J. M. Byrne

Abstract

The rooting substances of tomato (Lycopersicon esculentum Mill.) explants during root regeneration were studied. The root-promoting substances of the basic, acidic, and bound ether-soluble fractions of the plant extracts after paper chromatography were determined by a tomato hypocotyl test. The basic root-promoting substances in the basal hypocotyl region changed qualitatively, while those of the acidic and bound fractions decreased with rooting. It was found that in 5-day-old explants, the highest root-promoting substances were in the bound fraction, and in the basal hypocotyl region. Histological evidence showed the presence of preformed root primordia in the rooting region of 10-day-old tomato explants.