Dark-grown sunflower (Helianthus annuus L.) seedling hypocotyls (15-30 mm) were marked with two rows of lanolincoated resin beads, and the events of the following 24 hr, in physiological darkness, were recorded on time-lapse video. Nutational movement of the hypocotyl, followed for 20--24 hr for each of 21 seedlings, was found to have a mean period of 153 ± 26 min (ca. 24 C). Displacement of each bead, with time, was measured with a microcomputer-controlled video analyzer, and relative elemental elongation rate and relative growth rate analyses were carried out to determine the spatial and temporal distribution of growth. Relative elemental elongation rates were plotted against distance and time to produce "growth landscapes." A strongly nutating seedling showed periodic fluctuations in local growth rates that alternated between values of 0.0 hr-I and >0.12 hr-I near the hypocotyl hook. Nearer the base, maximum growth rates were lower but local periodic changes still were evident. Seedlings, in which nutation appeared during the time period analyzed, showed nonsynchronous pulses of growth along the axis. With nutational development, these local growth fluctuations became synchronized along each side and phased (usually 180· out ofphase) with the coordinated growth fluctuations along the opposite side. In some seedlings the changes from low to high local growth rates occur nearly simultaneously over two-thirds of the active region. In others, basipetally traveling waves of growth are suggested by the growth landscapes.

No abstract

The leaf initiation rate and apical volume growth rate of lateral shoots of Chrysanthemum morifolium 'Improved Albatross III' were determined for plants growing under controlled environment conditions. After removal of the terminal bud, the top two lateral buds produced leaves at a rate of 1.4 to 1.6 leaves/day for the first 9 or 10 days. At about the 10th day there appeared to be an abrupt shift to a lower initiation rate of 0.7 to 0.8 leaves/day. Defoliation by periodic removal of leaves larger than 1 cm caused a statistically significant increase in initiation rate, but not to as high a rate as that of the first 10 days of bud growth. Volume growth rates of the apical region were determined from transverse sections of five apices, according to the method of Richards (1951). The apical region was found to have a radial expansion rate of O.1623/plastochron and a vertical expansion rate of 0.0494/plastochron. The volume growth rate was calculated to be 0.3740/plastochron and the volume doubling time to be ] .8.,} plastochrons or 56 to 63 hr.

The growth responses of a sunflower seedling (Helianthas annus L.), subjected to repeated inversion, were characterized by time-lapse recording in coqjunction with video image analysis. The investigation revealed a characteristic response pattern and established that the directional movement of the seedling is achieved by both inhbiitio and stimulation of growth in the normal growing regions. The complex growth changes in contiguous regions of the hypocotyl are such as seem to be inexplicable in terms of an environmentally imposed gradient of a single growth substance.itself affect growth (1, 5), it is essential to avoid any extraneous disturbance ofthe plant, and a specially designed growth chamber in which the seedling could be smoothly rotated was used to minimize disturbance.Video recording of an experimental sequence has several advantages over cine photography, especially the fact that it is cheaper and also permits on-screen measurements to be made in real time. Moreover, a video camera has the potential for recording under IR radiation of >800 nm. The main advantage of the cine photography lies in the improved quality of photographic reproduction. Several experiments on the growth of inverted seedlings have been filmed with the video camera confirming the general pattern of response of the seedling described here, the growth of which had first been recorded with a cine camera to yield better quality photographs for illustrative purposes.

Koller, D., A. Poljakoff‐Mayber, A. Berg, and T. Diskin. (Hebrew U., Jerusalem, Israel.) Germination‐regulating mechanisms in Citrullus colocynthis. Amer. Jour. Bot. 50(6): 597–603. Illus. 1963.—Intact seeds from mature, dry fruits of Citrullus colocynthis, collected in the southern Negev desert, did not germinate under a wide variety of experimental conditions. This inhibition was imposed by the testa, since germination was made possible by mechanically forcing open the testa, or by its complete removal. However, various pretreatments, including some which modified or even pierced the testa, failed to effect germination. No inhibitors were found in the testa and the manner in which it inhibits germination is yet unknown. How this inhibition is overcome in nature is also unknown. Germination of decoated seeds was inhibited by continuous light in combination with temperatures below 25 C. Removal of the inner seed membrane removed this inhibition, but, growth of the naked embryos at all temperatures was greatly reduced by continuous light, which also strongly influenced early development. An intact inner seed membrane had no effect on germination in darkness, but inhibited it in light at temperatures below 25 C. Inhibitory effects of the inner seed membrane could be duplicated by enclosing the naked embryos in moist filter paper and are thus probably the result of an interference with exchange of respiratory gases between the embryo and the atmosphere. Very low light intensities sufficed to inhibit decoated seeds, but at least 12‐hr daily illumination was required to produce significant inhibition. The blue region of the visible spectrum, transmitted by green and blue cellophane filters, was the most inhibitory. The site of light perception was located in the radicular portions of the embryo.