Abstract Articles concerning the International System of Units have appeared in several plant science journals (4–6, 8, 9, 11). However, a cursory glance through leading American plant science journals, including HortScience and the Journal of the American Society for Horticultural Science , reveals that, while everyone is using the metric system, a large number of authors are not following the rules inherent in the International System of Units, commonly called SI. Metrics without SI is not much improvement over the firkin, barrel, and chain; failure to use the International System of Units simply changes the chaos of units from the fps (foot–pound–second) to the mks (meter–kilogram–second) system. Many examples of irregular units could be cited, including mg CO 2 ·dm –2 ·hr –1 , g H 2 O·dm –2 ·hr –1 , or their variations µmol CO 2 ·s –1 ·m –2 and mmol H 2 O·s –1 ·m –2 . Similar errors are noted in units like MT/ha, µg P/g soil, mg/100 g FW, mg·1000 cc –1 , and some rare ones such as ml/kg/hr. It seems reasonable to assume that the authors of the above units are not familiar with SI rules, chiefly because these rules have not been published in journals they customarily read. Therefore, publication of rules to follow when using SI terms should prove a useful addition to Savage's discussion of SI (10) and the efforts of ASHS committees to establish standards for reporting (5, 6).

A recent update supplement of the ASHS Publications Manual (1) states that photosynthetic photon flux density (PPFD) shall now be called photosynthetic photon flux (PPF). This decision appears to be based on a Feature article by Holmes et al. (2), which suggested that flux density was seriously misused to describe flux. They offered three definitions of flux to support this alleged misuse—Chamber's Dictionary of Science and Technology: the rate of flow of mass, volume, or energy per unit cross-section normal to the direction of flow; McGraw-Hill Dictionary of Scientific and Technical Terms: the amount of some quantity flowing across a given area per unit time; Oxford English Dictionary: the rate of flow of any fluid across a given area; the amount of which crosses an area in a given time; it is thus a vector referred to unit area.

Abstract Turnip ( Brassica rapa L.) growth in an unshaded, temperature-controlled greenhouse varied annually as a function of month. Growth was proportional to the average daily irradiance at plant level, but variance of the data suggested an interaction with some other environmental factor, possibly reduced substrate and plant temperature due to reradiation to the cold greenhouse glass at night during winter.

The growth rate of excised soybean (Glycine max [L.] Merrill) embryos grown in liquid culture increased linearly as photoperiod was increased from 0 to 20 h at an irradiance of 9 W m-2 measured between wavelengths of 700-850 nm from clear incandescent lamps. When irradiance levels were varied between 0.1 and 1.7 W m-2, the maximum growth rates of embryos occurred at ca. 0.5 W m-2 at both 10- and 16-h photoperiods. When the light source was changed from clear incandescent lamps, with a red (600-700 nm) to far-red (700-770 nm) ratio of ca. 1.07, to a BCJ incandescent lamp (Corning Glass dark red, transparent envelope and a red to far-red ratio of ca. 0.19), the growth rate of embryos slowed. These results are consistent with a high irradiance response for growth of soybean embryos.

Abstract The cause of the premature burn-out of incandescent lamps used in plant growth chambers was determined. Group replacement of lamps can be practiced on an annual basis with proper lamp selection.

AbstractTobacco (Nicotiana tabacum L.), essentially a nursery plant during seedling growth, is grown in a protected plant bed until it attains the size to be transplanted into the field. Enchancement of growth rates during seedling culture would have advantages in production of tobacco seedlings, as well as bedding plants. Enrichment of atmospheric CO2 is a generally recognized technique of increasing growth rates. Experiments were conducted in controlled‐environment chambers to evaluate the immediate effects of CO2 enrichment on seedling growth of tobacco, the carryover effects to post‐transplant growth, and nutritional requirements for maximum response to CO2 enrichment.Tobacco seedlings were grown at two rates of nutrient application in atmospheres containing either ambient (400 ppm) or enriched (1,000 ppm) CO2 levels. At the time of transplanting half of the plants from each CO2 environment were reciprocally exchanged. During seedling culture, Relative Growth Rate (RGR) was enhanced CO2 enrichment but was depressed by the higher nutrient application rate. The RGR to CO2 enrichment was reversed during post‐transplant culture. For either CO2 environment, RGR during seedling growth was nearly three‐fold RGR during posttransplant culture. The reduction in RGR with CO2 enrichment occurred for both a 9‐hour and a 15‐hour light period of 450 hectolux intensity. The lower RGR for CO2 enrichment during post‐transplant culture was associated with increased starch in leaf tissues. These data support the hypothesis that, although growth response may temporarily be enhanced by CO2 enrichment, it must decline to a level similar to that of plants raised under ambient CO2.

Nicotiana tabacum L. cv. Coker 319 has been found to be sensitive to changes both in temperature and photoperiod. Within a given time period fewer leaves are produced at low temperatures than at high temperatures. The classical day-neutral flowering response was not observed for this plant under six photoperiods of varying lengths. The results thus indicate that the plant may be more appropriately classified as being "preferentially ambiphotoperiodic," rather than strict "day-neutral." Preconditioning the seedlings with a long-day photoperiod produced plants that had higher total leaf numbers and flowered earlier than seedlings treated with a short-day photoperiod. The morphology of the vegetative and reproductive stem apex was similar to that reported for other species and cultivars of Nicotiana. Apical meristems were systematically ranked according to their progressive developmental stages encompassing vegetative, transition, and reproductive development.

AbstractPlants growing in controlled‐environment rooms are frequently subjected to self‐depleted CO2 levels that manufacturers' “make‐up air systems” do little to alleviate. Flue‐cured tobacco (Nicotiana tabacum L. ‘Coker 319’) rapidly depletes CO2 from a 400 ppm (μl/liter) ambient level of 200 ppm. When compared with plants grown to maturity in an atmosphere continually adjusted to the 400 ppm level by supplementary CO2, chemical assays of leaf constituents indicated lesser effects of the CO2 depletion than anticipated. The contents of starch, soluble carbohydrates, and polyphenolics were meagerly depressed in a CO2‐depleted atmosphere. A reduction in light intensity below 322 hectolux had a greater effect accumulation of these compounds than did CO2 depletion, The CO2 depletion did affect the composition of the soluble carbohydrate fraction in leaf tissue.The CO2 and light treatments in this experiment were continued until au advanced stage of leaf senescence. Both CO2 depletion and reduced light intensities prolonged the growth period of leaves before the onset of senescence. We conclude that the extended period of growth, as well as the chronological timing of other morphological eve:ats, explains many of our reported results.

AbstractTobacco (Nicotiana tabacum L. ‘Coker 319‘) plants were grown to maturity in the facilities of the North Carolina State University Phytotron (Southeastern Plant Environment Laboratory) to determine effects of temperature and light duration on the physical characteristics of fresh leaves. Leaf area, shape, and specific leaf weight (dry weight per unit leaf surface area) were determined at six stalk positions. The lower temperatures resulted in small, relatively wide leaves at the base of the plant and elongated leaves at the top. Higher temperatures tended to reverse the normal shape and size ordering sequence of leaves; at the highest temperature condition the largest, as well as the broadest, leaves were developed at the uppermost stalk positions. The specific leaf weight was increased by an increase in the duration of the high intensity light period and by decreases in temperature. The increased light duration also enhanced the relative width of leaves.

Effects of active phytochrome (Pfr) on flowering in cocklebur, Xanthium pensfivanicum Wallr., subjected to unusually short photoperiods were examined. For interpretation of the results, Pfr is considered to be an enzyme that catalyzes a reaction that controls many phenomena including flowering. In cocklebur plants phytochrome is in the Pfr form at the end of the photoperiod. After photoperiods of 11/2 or 2 hr the Pfr, although present, does not act during the first 6 or 8 hr of darkness. This failure is attributed to delay in arrival of substrate for Pfr action. Between the eighth and tenth hours Pfr acts to promote flowering. After the tenth hour it is no longer present, and, if it is then reintroduced by a red irradiation, it inhibits flowering. Dark reversion of Pfr is completed simultaneously with completion of its flower-promoting action and is regarded as a consequence of its action. The amount of radiant energy received by cockleburs during a 3-hr photoperiod determines whether Pfr action is necessary for promotion of flowering, the flower-promoting effect being exhibited only after photoperiods of low irradiance. The Pfr left in cockleburs at the end of 2-hr photoperiods thus plays no role essential to flowering during the first 8 hr of darkness During the next 2 hr it promotes flowering, and during several hours after that, Pfr is absent. If reintroduced during that time, it would be inhibitory.