15-hour Photoperiod Research Articles

Illuminating plant–microbe interaction: How photoperiod affects rhizosphere and pollutant removal in constructed wetland?

Rhizosphere is a crucial area in comprehending the interaction between plants and microorganisms in constructed wetlands (CWs). However, influence of photoperiod, a key factor that regulates photosynthesis and rhizosphere microbial activity, remains largely unknown. This study investigated the effect of photoperiod (9, 12, 15 h/day) on pollutant removal and underlying mechanisms. Results showed that 15-hour photoperiod treatment exhibited the highest removal efficiencies for COD (87.26%), TN (63.32%), and NO3–-N (97.79%). This treatment enhanced photosynthetic pigmentation and root activity, which increased transport of oxygen and soluble organic carbon to rhizosphere, thus promoting microbial nitrification and denitrification. Microbial community analysis revealed a more stable co-occurrence network due to increased complexity and aggregation in the 15-hour photoperiod treatment. Phaselicystis was identified as a key connector, which was responsible for transferring necessary carbon sources, ATP, and electron donors that supported and optimized nitrogen metabolism in the CWs. Structural equation model analysis emphasized the importance of plant–microbe interactions in pollutant removal through increased substance, information, and energy exchange. These findings offer valuable insights for CWs design and operation in various latitudes and rural areas for small-scale decentralized systems.

Metabolic Variations in Grass C. dactylon and Selection of Optimal LEDs for the Horticulture Luminaire Using LM Algorithm

Healing of various ailments using herbal medicines is gaining much interest. Plants classified as grasses, specifically Cynodon dactylon , are an appreciated group of monocots used in many herbal remedies. In this work, C. dactylon , is grown naturally and also under market available LED Luminaires with different lighting conditions. Until 2010, most of the plants are grown under conventional lamps that are not spectrally tunable. Cynodon dactylon , the grass is grown under two different light spectrum, two light levels and three photoperiods (9hours, 12 hours, 15 hours) to extend our experiential knowledge. The biomass accumulation was the highest when grown under a lower RB ratio-12-hour- $163\mu $ mol/s, and phenolic content was the highest at 92.8 mg/g wt Gallic Acid Equivalents under combined light source at 15-hour photoperiod. A spectrally tunable LED light source with an optimal quantity of LEDs saves cost, space and energy. Considering the light parameters from the light sources used for growing C. dactylon , Levenberg–Marquardt (LM) algorithm is implemented to select an optimal LED quantity that composes the light source. The algorithm simulates the given target spectrum with minimum fitness error. The method applied to model LEDs, its validation against the practical LED spectrum, spectrum matching and computation of Luminous flux, Photosynthetic Photon Flux and efficacy are also presented. Many spectrums are simulated to validate the performance of the algorithm. A solution of optimal LEDs for three Photosynthetic Photon Flux (PPF) levels with LEDs is derived, and it is observed that the number of LEDs increased with PPF.

Adaptations of Female Bobwhites to Energy Demands of the Reproductive Cycle

The energy required by bobwhites (Colinus virginianus) to attain reproductive condition was measured for 30 individually caged game-farm raised birds. They were acclimated to an eight-hour photoperiod, which then was increased one hour each week until reaching 15 hours; it was then kept constant. One hen began laying eggs five weeks after the 15-hour photoperiod started. However, only 75 percent of the birds that eventually layed were laying after 12 weeks at 15 hours photoperiod. Average body weights increased from 194.2 g seven weeks prior to egg laying to 214.8 g while laying. Metabolized energy increased 24.4 percent (35.6 to 44.3 kcal/bird-day) during the six weeks prior to the onset of yolk deposition, which occurs in the week prior to laying. Metabolized energy increased another 18.3 percent to 52.4 kcal/bird-day while the quail were laying eggs. These results show several adaptations of bobwhites that permit them to meet the energy demanding activity of achieving reproductive status. This asynchronous response to photostimulation enables the birds to optimize their time of lay to unpredictable weather conditions prevalent in spring in temperate climates. In addition, the energy required to achieve reproductive condition is spread over six weeks; thus, the impact of increased energy demands is minimized.

Effects of radiotransmitters on body mass, feed consumption, and energy expenditure of northern bobwhites

Radiotelemetry is commonly used in northern bobwhite (Colinus virginianus) research. An underlying assumption is that radiomarked individuals provide unbiased estimates of population parameters. Our objectives were to evaluate the effects of radiotransmitters on body mass and feed consumption of radiomarked and banded-only pen-raised bobwhites in a controlled environment and to compare daily energy expenditure (kJ/g/day) between treatments in a simulated field setting. We randomly assigned a treatment (i.e., radiomarked or banded-only) to 40 pen-raised bobwhites and placed them in individual cages (51- × 27- × 28-cm) within an environmental chamber. We conducted 2 separate 21-day experiments to simulate summer (35°C daytime high, 23.9°C nighttime low, 15-hour photoperiod) and winter conditions (18.3°C daytime high, 4.4°C nighttime low, 10-hour photoperiod) typical for south Texas. For the field experiment, we evaluated energy expenditure via doubly labeled water for radiomarked (n=5) and banded-only pen-raised bobwhites (n=5) in a flight pen (50- × 30- × 4-m). We documented no difference in change in body mass or feed consumption between radiomarked and banded-only bobwhites during either experiment (P>0.05). We also found no difference in daily energy expenditure between radiomarked (0.839 ± 0.056 kJ/g/day) and banded-only pen-raised bobwhites (0.804 ± 0.014 kJ/g/day; P=0.77).

Stratification and Light Improve Germination of Katsura Tree Seed

Germinability of two, half-sib seed sources of Cercidiphyllum japonicum Sieb. & Zucc. and one seed source of Cercidiphyllum magnificum (Nakai) Nakai was determined after not stratifying or stratifying seeds at 3.5 ± 0.5 °C (38.3 ± 0.9 °F) for 8 days followed by germination for 21 days at 25 °C (77 °F) in darkness or under a 15-hour photoperiod. Stratification was not required for germination, but increased germination percentage, peak value, and germination value for both species. Stratification increased germination of C. japonicum from 42% to 75%, and germination of C. magnificum from 12% to 24%. Light enhanced germination of nonstratified seeds of one source of C. japonicum and of C. magnificum from 34% to 52% and from 8% to 15%, respectively. Stratification improved germinability of both species and obviated any preexisting light requirements the seeds may have had.

Diurnal Growth of Tall Fescue Leaf Blades

Tall fescue leaf blades elongate at near constant rates during most of the light and dark periods of the diurnal cycle, with the dark rate being higher by 60 to 65%. Our objective was to determine relationships among diurnal rates of leaf elongation, deposition of water and deposition of dry matter (DM) into the elongation zone. Two separate experiments were conducted, both with a 15-hour photoperiod and constant 21 degrees C at the growth zone. Increased rates of leaf elongation in darkness were due to proportionally increased rates of elongation of 4-millimeter segments of the elongation zone. Length of the total elongation zone was 30 millimeters in both light and darkness. The spatial distribution of water contents in the elongation zone varied little during the diurnal cycle. Thus, dark stimulation of leaf elongation rate (+65%) and of water deposition (+77%) into elongation zones were similar. Water content per unit leaf length increased by 50% between the basal and distal limits of the elongation zone, indicating that tissue also grew in the lateral and vertical dimensions. Longitudinal growth of tissue, however, allowed 5 to 7 times more water deposition into the elongation zone than growth in cross-sectional area. This relationship was similar in light and darkness. In both light and darkness net rates of DM deposition (microgram per millimeter leaf length per hour) increased from the zone of cell division towards the region of most active elongation, 10 to 15 millimeters from the ligule, then decreased towards the distal end of the elongation zone. Net DM deposition rates (microgram per hour) integrated over the 30-millimeter elongation zone were similar during light and darkness. Thus, DM in the elongation zone was diluted during darkness as a result of increased water deposition. Net DM deposition rates at and above the distal end of the elongation zone were clearly positive during the light, but were close to zero or negative in darkness. Thus, DM deposition into the elongation zone and the adjacent recently expanded tissue was differentially affected in the diurnal cycle, DM deposition occurred in both tissues in light, but was restricted to the elongation zone in darkness.

Energetics of the Canada Goose

Measurements of food use in captive Canada geese (Branta canadensis interior) over 3to 4-day periods at constant temperatures showed that existence metabolism (Mkcal = kcal/bird/day) increased with drop in temperature (T = ?C) as: Mkcal = 511 4.983T in males at 10and 15-hour photoperiods and Mkcal = 487 4.709T in a female at 15-hour photoperiod. The metabolizable energy coefficient averaged 75.6%. Lower limits of temperature tolerance were below -40 C and upper limits approximately +41 C. Geese held out-of-doors exhibited many of the same fluctuations in weight during the year as occurs in wild populations. The first phase of annual molt involved replacement of flight feathers, and at this time weight reached its minimum. Replacement of body feathers began as flight feathers neared full growth and body weight increased. Maximum weights were attained in April. A change of 1 gram/day in body weight was correlated with a change of 3.4 kcal/bird/day. Total diel and nocturnal cage activity increased along with weight during the migration periods. Carcass analyses showed that body lipids became reduced at low temperatures and body water at high temperatures. Minimum lipid reserves occurred in molting geese with maximum levels in spring. A nearly constant level of existence metabolism and potential productive energy is maintained by migration between breeding and wintering areas. J. WILDL. MANAGE. 46(3):588-600 The present study, conducted from 1959 to 1963, was designed to investigate the energy economy of the Canada goose in relation to variations in temperature and photoperiod to which it is subjected during its annual cycle. The objective was to obtain direct quantitative information of the role of energy in limiting distribution and regulating migration. The use of experimental data from birds under controlled conditions for explaining behavior of free-living birds under natural conditions must be made with caution but provides an understanding of underlying physiological potentials. We thank H. C. Hanson of the Illinois Natural History Survey who, in addition to many valuable suggestions, made the geese available, classified them to sex and age, and supplied some of the experimental equipment. D. G. Raveling provided helpful suggestions for revising the final manuscript. Appreciation is expressed to R. Williams for help in analyzing portions of the results and to A. Kosowski, J. B. Olson, J. Zar, N. Arnoldi, F. H. Blackmore, and D. Parrack for their contributions to various portions of the experimental work. L. C. Bliss and J. Kastelic made laboratory facilities available. This research was financed by a grant from the National Science Foundation to S. C. Kendeigh.

The effects of growth substances and photoperiod on the development of shoot apices of Vitis cultured in vitro

‘Rougeon’ grapevines were recovered from shoot apices using in vitro culture. Shoot development from apices 0.5–1 mm in length, which contained 2–4 leaf primordia was obtained with 5 × 10 −6M benzylaminopurine and 5 × 10 −7M naphthaleneacetic acid (NAA) under a 10-hour photoperiod, but not under continuous light, in a 15-hour photoperiod, or in darkness. At least one vigorous shoot was produced by 100% of the cultures. Rooting of these shoots was induced under the same photoperiod with the same basal culture media containing only 10 −7 M NAA. Roots were produced by 91% of the cultures. Zero-, 16- or 24-h photoperiods were ineffective in promoting root development. Rooted plantlets were transferred into soil with 80% of them surviving. The grapevines were allowed to reach an average length of 2 m in a growth chamber before growth conditions were modified to induce dormancy. Vines were planted in a vineyard; after 2 growing-seasons we were unable to distinguish the micropropagated vines from ‘Rougeon’ vines propagated in the standard manner, on the basis of fruit or vegetative morphology.

Photosynthetic Rates of Citronella and Lemongrass

Ten selections of citronella (Cymbopogon nardus [L.] Rendle) were grown at 32/27, 27/21, or 15/10 C day/night temperatures, and plants from three populations of lemongrass (Cymbopogon citratus [D.C.] Stapf from Japan or Sri Lanka and Cymbopogon flexuosus [D.C.] Stapf from India) were grown at 8- or 15-hour photoperiods. Net photosynthetic rates of mature leaves were measured in a controlled environment at 25 C and 260 microeinsteins per meter(2) per second. Rates declined with increasing leaf age, and from the tip to the base of the leaf blade. Rates for citronella leaves grown at 15/10 C were extremely low for all selections. Highest rates of net photosynthesis were recorded for four selections grown at 27/21 C and for two selections grown at 32/27 C. Lemongrass grown at 8-hour photoperiod had higher photosynthetic rates than that grown at 15-hour photoperiod.

Carbon Dioxide Compensation Values in Citronella and Lemongrass

Carbon dioxide compensation values of mature leaves from 10 selections of citronella (Cymbopogon nardus [L.] Rendle) grown at 32/27 or 27/21 C day/night temperatures and three strains of lemongrass (Cymbopogon citratus [D.C.] Stapf. and Cymbopogon flexuosus [D.C.] Stapf.) grown at 8- or 15-hour photoperiods were measured in a controlled environment at 25 C. All leaves had low compensation values but citronella varied from 1.3 to 9.7 mul/liter and lemongrass from 0.7 to 3.5 mul/liter. Lower growing temperature generally resulted in lower compensation values for citronella but there was no consistent photoperiod effect on lemongrass.

Circannual Rhythmicity and Entrainment of Surface Activity in the Hibernator, Perognathus longimembris

Long-term patterns of surface activity were monitored in 15 pocket mice, Perognathus longimembris , which constructed burrow systems in dirt-filled terrariums kept at 16°c and 31°c on 12-hour photoperiods. a rhythm, with an average period of about 10 months, was evident in the behavior of the mice at 16°c. During each cycle, these animals spent several months continuously underground even though food was always available on the surface. The transition between the underground and surface active phases of the cycle was usually gradual. However, the mice immediately resumed nightly foraging if the upper layers of the soil were heated each day during this transition time. They did not respond to this stimulus during the middle of the underground phase of the annual cycle. I suggest that in nature the vertical uniformity of soil temperatures in the spring may cue the synchronization of the circannual rhythm with the seasons. The absence of surface activity is apparently unrelated to torpor because mice at 31°c, where torpor does not occur, also spent several months continuously underground. However, the regular 10-month periodicity of the behavioral cycle was disrupted in this hot environment. Torpor was also monitored for up to 20 months in 25 mice at 8°c and 18°c under 9-hour and 15-hour photoperiods, but circannual rhythms of torpor were not evident under these experimental conditions.

Rearing and Release of Microctonus aethiops, a Parasite of the Alfalfa Weevil, in Maryland123

Larvae of the alfalfa weevil, Hypera Postica (Gyllenhal), were reared at 25.6°C and with a 15-hour photoperiod. Following emergence, adults were active for 2-3 weeks before entering diapause. During this period, weevils were exposed to parasites, and at a parasite-host ratio of ca. 1:50 survival of weevils averaged 93%. Diapausing pausing parasitized weevils were stored successfully at 10°C. Topical applications of a synthetic juvenile hormone, a mixture of cis,trans and trans,trans -10,11-epoxyfarnesenic acid methyl ester, were used to break diapause in hosts and coordinate emergence of parasites so that a large number of Microclonus aethiops (Nees) would be available for release within a short time interval. Parasites were released either as adults (ca. 100 mated females/field) or as larvae within hormone-treated hosts. The adult-release method was superior. M. aethiops was released at 5 sites in Maryland where it was determined previously to be absent. It was recovered at Germantown, Montgomery County; Boonsboro, Washington County; and Butler, Baltimore County. The parasite was reported previously to have established itself in 6 additional eastern and northern counties of Maryland, apparently as a result of dispersion from Delaware and Pennsylvania.

PHOTOPERIODICALLY INDUCED TESTICULAR RECRUDESCENCE IN THE TRANSEQUATORIAL MIGRANTDOLICHONYXRELATIVE TO NATURAL PHOTOPERIODS

1.Dolichonyx oryzivorus, the bobolink, breeds in North America in June and July and spends the months of November through March in South America below the equator. Ninety-six males captured during migration were held in an outdoor aviary at Chapel Hill, North Carolina (Latitude 36° N) until start of artificial lighting. 2. Beginning in early October, they were exposed daily to 12.5-hour photoperiods for five weeks to terminate photorefractoriness. Thereafter, different groups were subjected to daily photoperiods of 14, 15, 16, 17 and 18 hours. These groups were sampled at intervals and progress of testicular recrudescence was determined by gonadal weights. 3. Evidence adduced from museum specimens indicates that testicular recrudesence begins about the end of March. In the experiments, recrudescence seemingly was initiated immediately, in November, on the longer photoperiods and proceeded at rates comparable to those shown by a temperate-zone migrant. Drastically different was the response to 14-hour photoperiods, initiation of recrudescence being delayed for ten or more weeks. 4. In South America bobolinks occur between Latitude 8° S and Latitude 30° to 35° S. Day-lengths at these latitudes never exceed 15.5 hours; so even at the December solstice males are not exposed to the longer photoperiods which brought about immediate recrudescence in the experiments. Because bobolinks do not come into breeding condition in the southern hemisphere, this response is viewed as a limiting factor in southward distribution. But since 15-hour photoperiods also induced early recrudescence, one would not expect the species to go as far south as Latitude 30° to 35°. This is the most puzzling lack of fit of the experimental results to nature. 5. Although 14-hour photoperiods greatly delay the onset of recrudescence, they do induce it earlier than its occurrence in nature, even though they are somewhat shorter than the average day-length occurring at the latitudes in the middle of the bobolink's winter range. Thus there is at best an imperfect fit of the experimental results to the normal timing.

PHOTOPERIODISM IN THE DEVELOPMENT OF THE EUROPEAN PINE SAWFLY, NEODIPRION SERTIFER (GEOFF.).

Photoperiods of 0 to 24 hours at 21 °C did not influence the length of the larval developmental period of N. sertifer or the weight of larvae at cocoon spinning. Upon incubation of cocoons in darkness, most of the larvae from 4- to 15-hour photoperiods metamorphosed without an intervening prepupal diapause, and emerged as adults 27 to 35 days after cocoon spinning. Individuals from the 0-, 20-, and 24-hour photoperiods underwent a prepupal diapause of 2 to 3 weeks before morphogenesis, and emerged as adults 44 to 55 days after cocooning. The transition from diapause to non-diapause is induced by a photoperiod of about 16 hours.

Stoffwechselreaktionen süßwasserlebender Sonnenbarsche auf jahreszeitliche Photoperioden und Temperaturen

1. Metabolic compensations by pumpkinseed sunfish,Lepomis gibbosus, to photoperiods of 9 and 15 hours and to acclimation temperatures ranging between 5° and 25° C have been examined. Respiration rates of whole fish, their brain, gill and muscle tissues, and opercular frequencies were used as indices of adaptation. Techniques for the determination of respiration rates and opercular frequencies have been outlined and discussed. 2. A range in thermal homeostasis has been found forL. gibbosus over which thermal acclimation of respiration is nearly perfect (Q 10 about 1), but which is modifiable by alterations in day length above 10° C. Although less obvious, a relative thermal homeostasis has been detected for opercular frequency as well. Perfection of acclimation appears to be best with both indices in the groups of sunfish which have been adapted to the 15-hour photoperiod. 3. Significant differences in rates of respiration, but not in opercular frequencies, have been observed between the long and short-day groups of fall and winter sunfish above 10° C. During spring and with sunfish in breeding condition, these differences were not detected. Both short and long-day fish showed the same higher level of respiration found to be related to short photoperiod adaptation (9 hrs.). It is suggested that the photoperiodic effect of inducing changes in metabolic rates, most directly relates to some process of conditioning the fish for their primary biological function, reproduction. 4. Because the characteristics and photoperiod sensitivity of metabolic compensations for temperature byL. gibbosus are not apparent below 10° C, this temperature is considered to be critical ecologically for the species in western Massachusetts. The existence of a lower critical temperature for thermal homeostasis of metabolic functions (capacity adaptation) in sunfish is stressed because of its potential as a sensitive indicator of physiological variations for climate and latitude. 5. No indications of compensation for photoperiod (9 and 15 hrs.) and temperatures (7.5° and 20° C) have been detected in the respiration of brain and gill tissues ofL. gibbosus at 25° C except after uncoupling with dinitrophenol. The response of brain respiration with the drug appears to be greatest in sunfish adapted to a 9-hour day and 20° C. In contrast, the dinitrophenol effect upon respiratory change of gill filaments appears to be reversed with respect to the thermal history of the donor fish (highest with acclimation to 7.5° C), but unrelated to the length of the adaptation photoperiod. It is apparent that metabolic systems in different tissues of the same animal or the same tissues in different species, contrast greatly in compensatory responses to temperature and photoperiod. Therefore, the suggestion is offered that the resultant of systemic integration often may be more significantly reflected in responses of whole fishes to changing environmental factors than the possible direct effects of temperature sometimes seen in isolated tissues.

THE EFFECTS OF PHOTOPERIOD, TEMPERATURE, AND LIGHT INTENSITY ON THE GROWTH OF THE LOWBUSH BLUEBERRY (VACCINIUM ANGUSTIFOLIUM AIT.)

A study of the effect of environmental factors on the growth and development of the lowbush blueberry was carried out using clonally propagated plants. In a preliminary study a definite photoperiodic response was found. Under 8-hour days flower buds were formed and no vegetative growth occurred. Under 16-hour days vegetative growth resulted and no flower bud formation occurred. In a replicated greenhouse experiment, seven clones produced flower buds with 8-, 10-, and 12-hour days, but produced none with 14- or 16-hour days. One clone produced flower buds with 8-, 10,- 12-, and 14-, but none with 16-hour days. Two clones were able to produce flower buds under all five photoperiods. Under 8- and 10- hour photoperiods no vegetative growth occurred. Under 12, 14, and 16 hours progressively more vegetative growth occurred. In an experiment on the interaction of temperature and photoperiod, vegetative growth was significantly greater at 70° F than at 50° F with the differences being accentuated by day length. Flower bud formation occurred with 11- and 13-hour photoperiods regardless of temperature, but was more pronounced at the higher temperatures. At 70° F, 15-hour photoperiod, no flower buds were formed while at 50° F, 15 hours, three clones produced no flower buds and six clones produced an abnormal type of inflorescence. Similar abnormal inflorescences were produced by giving plants 2, 3, or 4 weeks of 8-hour days. Six weeks of 8-hour days was sufficient to initiate normal inflorescences. Shade, provided by two layers of cheesecloth, significantly reduced the number of flower buds compared with full sunlight. The growth of the lowbush blueberry under field and laboratory conditions is discussed in relation to environmental factors.

Hypothalamic neurosecretion in the refractory and post-refractory periods and its relationship to the rate of photoperiodically induced testicular growth in Zonotrichia leucophrys gambelii.

1. In late summer and autum many temperate-zone birds pass through a refractory period during which testicular growth cannot be induced experimentally with long daily photoperiods. This phenomenon is caused naturally by the long days of spring and early summer. It involves a decrease in release of gonadotropins by the adenohypophysis. Since previous investigations indicate that the release of gonadotropin is mediated by the hypothalamic neurosecretory system, a study of neurosecretory activity during refractoriness is basic for the understanding of this phenomenon. 2. Preliminary morphological studies on refractory birds revealed lateral divisions of neurosecretory cells lying between the supraoptic and paraventricular nuclei regions previously described (Okscheet al. 1959). Neurosecretory axons from these divisions join the tracts which pass to the median eminence. 3. Birds maintained in outdoor aviaries and killed from May through September showed a pronounced increase of neurosecretory material in the median eminence in late June, when testes regressed. This was accompanied by increases in neurosecretory material in the tracts and lateral division of neurosecretory cells described above, with reduction in sizes of cells and cell nuclei. The amount of neurosecretory material in the supraoptic nucleus was variable, but showed some increase, and the cells, again, decreased strikingly in size. 4. A series of birds was killed in the field from September through December. In the first part of this period there were considerable quantities of neurosecretory material in the median eminence. A pronounced reduction occurred in mid-October shortly before the earliest date at which positive testicular responses to long daily photoperiods have been obtained experimentally. The pathways from the lateral divisions of neurosecretory cells contained material initially (September) and at the end of the period (December) but were empty in late October and early November. The lateral divisions of neurosecretory cells contained minimal quantities of neurosecretory material at this time; the cells and nuclei appeared larger. Cells of the nucleus supraopticus contained variable amounts of neurosecretory material, but cells and nuclei reached a maximum in size, and presumably in activity, in late October and early November. 5. In studies of photoperiodic testicular response, birds were tested with 15-hour and 20-hour photoperiods at intervals from September through May. A positive response to long daily photoperiods first appeared in late October and early November. In adult birds the rate of response to 15-hour photoperiods was initially low, but increased significantly over November–December. The response of first-year birds (i.e. birds hatched during the previous summer) to 15-hour photoperiods proved difficult to interpret. On 20-hour photoperiods, however, the testicular growth rate was initially low, and increased significantly over November, December and January to an apparent maximum for this day length. 6. It is suggested that during refractoriness a factor required for the synthesis and/or release of gonadotropins cannot be transferred from the axons of the median eminence via the portal capillaries to the adenohypophysis in sufficient quantities to cause a testicular response. The inhibition at the level of the median eminence expresses itself histologically as an accumulation of neurosecretory material in the hypothalamus and a reduction in the amount of cytoplasm and the size of cell nuclei in neurosecretory regions. This inhibition sinks below an effective level for complete refractoriness in middle and late October, while days are still long enough to cause some activity of the neurosecretory system. This minor resumption of activity in autumn is probably associated with the autumnal gonadal recrudescence observed in some species. The reduced rates of testicular response obtained experimentally in November–December are attributed to persistent low-level activity of the inhibitory process. The reduced activity of the neurosecretory system after late autumn in wild birds is apparently attributable to the essentially nonstimulating effect of the shorter day lengths of this season.

Growth and Development in Range Grasses. V. Photoperiodic Responses of Clonal Divisions of Three Latitudinal Strains of Side-Oats Grama

1. Clonal divisions of twelve selected individuals of each of three strains of side-oats grama were grown from April 16 to November 17, 1944, on Chicago natural daylength and on photoperiods of 13, 14, and 15 (or more) hours. The three strains from Texas (San Antonio), Oklahoma (El Reno), and North Dakota (Cannonball) represent the extremes and approximate means of latitudinal origin and range of response of twelve strains previously grown over a 2-year period on 9-, 13-, 16-, 20-hour, and natural photoperiods. The selected individuals sampled the diversity of each strain. 2. All clones from Texas flowered rapidly and persistently on 13-hour photoperiod, and in late September on natural photoperiod. Some flowered weakly in September and October in the 14-hour series. None flowered in the 15-hour series. Vegetative growth was vigorous on all treatments. These clones are intermediate- or short-day plants with an upper critical photoperiod for rapid and vigorous flowering between 13 and 14 hours. All clones from North Dakota grew and flowered vigorously on natural, 14-, and 15-hour photoperiods. On 13-hour photoperiod growth was very limited, although some clones flowered weakly. These clones are long-day plants with a critical photoperiod for vigorous growth and flowering between 13 and 14 hours. Most clones from Oklahoma flowered equally well and fairly rapidly on 13- and 14-hour photoperiods. Most of them eventually flowered on natural photoperiod, but were delayed, in contrast to the 13- and 14-hour series. Most of them either failed to flower or were delayed in flowering on 15-hour photoperiod. These data and previous observations indicate that this strain includes both intermediate- and long-day plants, both types having a short critical photoperiod between 9 and 13 hours. One of the former has an upper critical photoperiod between 14 and 15 hours. 3. Such strong photoperiodic differentiation and adjustment have seldom been reported within a single native species. The series of photoperiodic types within it raises interesting questions as to the evolution and nature of the responsible genetic and physiological mechanisms, since the species probably originated in low latitudes, where the short-day response is typical, with subsequent adjustment to the longer days encountered in the northward extension of its range. Other implications of the findings discussed in this or the preceding paper (6) concern some of the causes of the morphological diversity among the latitudinal strains when grown together, as reported by other workers, and the bearing of photoperiodic adjustment upon possible acclimatization of strains to latitudes lower or higher than their native ones.

Photoperiodicity of Baeria chrysostoma

1. Baeria chrysostoma is a long-day plant, provided it is grown below 25⚬C. It will grow at light intensities of above 150 f.c., obtained with fluorescent tubes, and responds rapidly to long photoperiods. 2. At least 5 long photoperiods are required for flower initiation, and a 15-hour photoperiod is effective. Plants become sensitive to long photoperiods 5 days after germination; and a few days after the long photoperiodic treatment, microscopic observation shows flower initiation. 3. The intensity of the supplementary light required after an 8-hour photoperiod for flower initiation is above 100 f.c. Both the short and the long wave lengths are effective, but green light is not. The cotyledons and leaves are equally effective in perception of the light effect. 4. No extracts or pure substances induced flowering in plants kept on short photoperiods.