Sterling B. Hendricks

X‐Ray Interference in Partially Ordered Layer Lattices

The x‐ray interference is calculated for layer lattices in which the phase shifts between consecutive layers and the scattering powers of individual layers do not follow a strictly periodic arrangement. In the second section the scattering power of all layers is assumed to be the same but the phase shifts can take on different values. In the third section neither the scattering powers nor the phase shifts have fixed values but a simplifying assumption is made about the phase shifts according to which distances between neighboring layers can be represented as sums of two distances characteristic of the individual layers. In both these sections a random sequence of the layers is assumed. In the fourth section the problem of arbitrary scattering powers and phase shifts is treated, and furthermore a statistical correlation between neighboring layers is introduced. In the following section the general theory is applied to a specific partially ordered stacking of layers encountered in micas and other similar minerals. The last section treats irregularities in close packed structures of spheres and irregular sequences of layers in graphite.

Action of Light on Lettuce-Seed Germination

1. The observations of Flint and McAlister that imbibed seed of some lettuce varieties can be promoted in germination by irradiation in the red portion of the spectrum and inhibited in the infrared were verified. 2. The action spectra for promotion and inhibition were measured in detail for wave lengths greater than 4000 A. Maximum sensitivity for promotion was found in the region 6400-6700 A (red) and for inhibition in the region 7200-7500 A (infrared). 3. Absorption of radiation in the red or in the infrared region changes the effective pigment into the infrared- or the red-absorbing form, respectively. The alternation of form can be repeated many times. 4. The action spectrum for lettuce-seed germination is the same as that effective for photoperiodic control of floral initiation. The two phenomena involve the same initial photoreaction. 5. The photoreaction involves monomolecular isomerization of the effective pigment. 6. A reaction by which the pigment changes from the infrared- to the red-absorbing form occurs in darkness. This reaction was elsewhere found to be the one by which duration of darkness is measured in photoperiodic control of floral initiation. 7. Seed of one lettuce variety, Great Lakes, that did not require radiation for germination, became sensitive to radiation when held imbibed at 35⚬ C.

ACTTON SPECTRA OF PHYTOCHROME IN VITRO

Summary First‐order rate constants, Kλ, for the photochemical conversions of both forms of phytochrome, PR and PFR, were measured at various wavelengths between 300 and 800 nm. The product of the extinction coefficient, ε, and the quantum yield, ø, at any wave‐length, λ, could be determined from the value of Kλ and the mole fractions of PR and PFR present at the photostationary state set by λ. The determination of the action (εø) spectra required that the photostationary states in red and far‐red light be known. These were determined from the absorption spectra and kinetic data.

Electron Diffraction by Gases

The method of electron diffraction is used for determining the C–O–C valence angle (α) in 4,4′ diiododiphenyl ether [(C6H4I)2O] and the molecular structures of phosphorus (P4) and arsenic (As4). The electron diffraction photographs were analyzed by four different methods as follows: (1) Visual measurements, (2) measurements of densitometer records, (3) conversion of densitometer records into relative intensity curves, (4) comparison of transformed intensity curves obtained by multiplying the intensity of scattering by [(1/λ) sin θ/2]2 which produces prominent maxima for measurement. The valence angle α was found to be 118±3° for 4,4′ diiododiphenyl ether, definitely greater than the oxygen valence angle found for simpler types of molecules. Phosphorus and arsenic molecules were found to have a regular tetrahedral structure within the limits of experimental error, the atomic separations being 2.21A and 2.44A, respectively, [methods (1) and (2) were used for the case of arsenic]. The minimum atomic distance...

Action Spectrum for the Photoperiodic Control of Floral Initiation of Short-Day Plants

1. The purposes of this investigation were to obtain quantitative data on the photoreactions that prevent flowering of short-day plants, from which an action spectrum relating wave length to photoperiodic effectiveness of light could be derived, and to draw such inferences concerning the nature of the photoreactions as the action spectrum would permit. 2. Experiments designed to give the action spectrum made use of a specially designed prism spectrograph having a dispersion of 15 A. per cm. at 5000 A. At this wave length and with an effective slit width of 100 A. the energy was about 3000 ergs per sq. cm. per second with the slit illuminated by a carbon arc operated at 12 kw. input. 3. Plants investigated were soybean, Soja max (L.) Piper var. Biloxi, and cocklebur, Xanthium saccharatum Wallr. To facilitate irradiation, the foliar surface of the plants of each species at the beginning of an experiment was reduced to a single leaflet or leaf, respectively. 4. The experimental treatment was based on the fact that flowering of short-day plants receiving short photoperiods can be prevented by interrupting each of the accompanying long dark periods at or near the middle with a brief period of irradiation. In these experiments minimal energies required to prevent floral initiation were determined for many narrow regions of the spectrum. 5. The reciprocity law was tested and found to hold for the factors of time and intensity within the ranges used for dark-period interruption. Flowering response of both soybean and cocklebur depends on the total radiant energy used to interrupt the dark period. 6. Minimal energies necessary to prevent flowering depend upon the number of hours of darkness elapsing before the plants are irradiated but are constant over a 2-hour period beginning 30 minutes before the middle of the dark period. 7. Action spectra for soybean and cocklebur are similar in several respects. The limit of effectiveness of radiation for preventing flowering of both plants is near 7200 A., at the red end of the spectrum. Maximum effectiveness for both plants occurs over a broad region extending from about 6000 to 6800 A. A minimum of effectiveness of radiation for both plants occurs in the region of 4800 A., and effectiveness increases again at shorter wave lengths in the visible portion of the spectrum. 8. Ratios of energies required to prevent flowering in the regions of maximum and of minimum effectiveness were different for the two plants, being about 1:200 for cocklebur and 1:60 for soybean. 9. The possibility that chlorophyll may be the effective pigment in the photoperiodic reaction is examined.

Leaflet movement of Mimosa pudica L. Indicative of phytochrome action.

Summary1.Closing movements of Mimosa pudica pinnae, upon change from light to darkness, depend upon the presence of phytochrome in the far-red-absorbing form.2.The potentiated control of closing movements by phytochrome can be repeatedly established and reversed by repeated alternations of red and far-red radiation, respectively.3.Action spectra were measured for the potentiation of closure and for its reversal.4.The response to phytochrome action is evident in 5 minutes and is fully expressed in 30 minutes.5.This rapid response and the more rapid potentiation with half times of less than 1 minute for several other responses to phytochrome action indicate that the primary action of phytochrome ist not gene activation, but rather metabolic control at the substrate level.

Action Spectrum for Photoperiodic Control of Floral Initiation of a Long- Day Plant, Wintex Barley (Hordeum vulgare)

1. Wintex barley grown with an 11.5-hour photoperiod and a 12.5-hour dark period remained vegetative. If the dark period was interrupted with a brief period of irradiation of sufficient intensity, spikelet formation was stimulated. 2. By use of this technique of interrupting the dark period, quantitative data on the photoreaction that promoted flowering were obtained, and action spectra relating wave-length to photoperiodic effectiveness of light were derived. 3. The most effective time to apply the dark-period interruptions was the 2-hour period beginning 6.5 hours after the start of the dark period. Within this time and with the intensities used, the reciprocity law held. Energy required to promote flowering, if applied continuously throughout the 12.5-hour dark period, was about tenfold greater than if applied within the 2 hours near the middle of the dark period. 4. The action spectrum for the production of spikes in barley was very similar to the action spectra for the prevention of floral initiation in soybeans and in cocklebur. The long-wave-length cut-off beyond 7200 A, the positions of maximum effectiveness between 6000 and 6600 A, and the region from 5000 to 5600 A, in which effectiveness changed rapidly with small changes in wave-lengths, coincided very closely. Minimum effectiveness occurred near 4800 A for all three plants. 5. The elongation of barley stems was closely correlated with spike development. 6. The action spectra indicated that essentially the same pigment was involved in transferring energy to the photoperiodic reaction both in long-day and in short-day plants. 7. A working hypothesis based on the assumption that flowering both in long-day and in short-day plants is controlled by the same substance and that effectiveness is due to optimum concentration is discussed.

Action Spectrum for the Photoperiodic Control of Floral Initiation of the Long-Day Plant Hyoscyamus niger

1. Vegetative plants of Hyoscyamus niger can be induced to flower by application of relatively small amounts of radiant energy near the middle of dark periods that would prevent flowering if uninterrupted. 2. Interruptions of 12-hour dark periods with energies corresponding to about 100 foot-candle-minutes of light were effective in causing initiation of flower primordia. Minimum energy to cause a given effect was relatively constant if the interruption was made during the 2-hour period following the middle of the dark period. 3. The action curve for floral initiation of H. niger was readily established in the region from 7300 A to 5600 A. Limitation of energy from 5600 A to 4000 A made it impossible to establish a continuous response curve for this region, but sufficient points were obtained to establish the limits of effectiveness. This curve is essentially the same as those for control of flowering in soybean, cocklebur, and barley, and for regulation of leaf size in etiolated peas. 4. Similarity of the action curve for control of initiation of flower primordia in Hyoscyamus to the absorption of phycocyanin was noted, and the possibility that the effective pigment for the photoperiodic reaction might be some type of straight-chain tetrapyrrole was pointed out.

Overcoming dormancy in seeds with ethanol and other anesthetics.

Dormancy in fall panicum (Panicum dichotomiflorum Michx.) caryopses (seeds) is overcome by imbibition at 35° C in ethanol solutions. Whereas germination in the absence of ethanol depends on active phytochrome, the seeds may germinate in darkness after treatment with 0.2 to 0.5 M ethanol. Ethanol overcomes dormancy also in seeds of several other weedy grass species. Ethyl ether, chloroform, methanol, and acetone act similarly to ethanol. We suggest that this action depends on modifyng the properties of a membrane(s) in a manner related to the actions of other anesthetics.

Photocontrol of Mimosa pudica L. leaf movement.

Summary1.Mimosa pudica L. pinnae close in darkness when phytochrome is predominantly in the far-red-absorbing form (Pfr) and remain open when Pfr is low [6]. The leaflets remain open, however, in normal light periods irrespective of the form of phytochrome. Pinnae, after closing in darkness, regularly reopen in light.2.An action spectrum for the opening response shows maxima for effectiveness near 710 and 480 nm. This action spectrum is similar to that for a high-energy response affecting morphogenesis in many plants.3.Dropping of the petiole of M. pudica can be photostimulated by irradiation of the primary pulvinus after holding the plants in darkness [4].4.The photostimulation of the primary pulvinus is effective only at wavelengths less than 520 nm. Wave bands in the region of 400 to 470 nm are about equally effective.5.These photoresponses of M. pudica are related to current discussion about the nature of the high-energy and phytochrome photomorphogenic reactions.