Osmotic sensitivity in relation to salt sensitivity in germinating barley seeds

Abstract Cultivars of barley (Hordeum vulgare L.) were tested for germination sensitivity to progressively higher concentrations of salt, mannitol, and betaine. The three solutes were equally inhibitory at equal osmotic potential, but there was a consistent difference in osmotic sensitivity between two cultivars, CM-67 and Briggs (Briggs was the most sensitive). There was no difference between the two cultivars in salt or water uptake from salt solutions during imbibition. Brief presoaking in water did not improve salt resistance, indicating that a hydration-dependent decrease in membrane permeability is not involved in salt tolerance. The calcium content of Briggs was higher than CM-67. These results suggest that salt inhibits barley germination primarily by osmotic effects, and that salt influx during imbibition does not play a role in this inhibition. A hypothesis regarding salt effects on germination is discussed.     

TESTS OF SYNERGISM BETWEEN NICOTINE AND THE PYRETHRINS

Synergism between nicotine and pyrethrum applied by injection to adult Oncopeltus fasciatus Dal. has been reported by Turner (1951).
When these insecticides were applied alone and as a mixture to adult Tribolium castaneum Hbst., using a dipping technique, the data indicated that independent joint action occurred. Similar action could be eliminated because the two insecticides had varying relative potency.
Since the effect of the pyrethrins has been short-lived in some insects, it was postulated that the absence of synergism might be caused by failure of the nicotine to reach a site of action while the pyrethrins were still acting.
Application of nicotine, followed later by treatment with pyrethrins, gave evidence of synergism. A test in which the interval between treatments was varied from ¾ to 6 hr. showed that toxicity was greatest with the shortest interval between applications, and evidence of synergism had practically disappeared after 6 hr. The maximum amount of synergism observed was about twofold.     

Penetration of light into soil and its role in the control of seed germination

Abstract Light transmitted through soil, and the leaf litter of two tree species, was measured using a spectroradiometer. In general, a greater penetration by longer wavelengths, especially far-red, was noted. This was most marked in a dry sand sample. The effect was less in the case of clay-loam aggregates. Moisture in the samples had an opposite effect in these two cases, causing an increase in transmission through sand but a decrease through clay loam aggregates. Reduction in particle size was found to reduce both the total light transmitted and the red/far-red ratio (R : FR). Red wavelengths were also more attenuated by a layer of freshly fallen oak (Quercus rotrur) leaves than were far-red wavelengths. A layer of Corsican pine (Pinus nigramaritima) needles however, was found to act as a neutral density filter over the 400 800 nm range. Prolonged exposure to soil-filtered light was found to affect the germination of seven species tested. Plantago major demonstrated an approximately linear decrease in germination with increasing depth. Rumex obtusifotius showed an apparent threshold response at 4 6 mm depth, as did Cecropia obtusifolia but at a slightly greater depth. Digitalis purpurea germinated very poorly in darkness, yet was extremely photosensitive with very high germination even at 10 mm depth. Galiutn aparine and Chenopodium album showed a two-phase response with germination reaching a peak at 2 mm depth. The implications for the function of the photoreceptor phytochrome in the control of germination are discussed in relation to soil-transmitted light and with regard to the results of the germination tests.