Seedlings of Lolium multiflorum Lam., Lespedeza stipulacea Maxim., and Buteloua curtipendula (Michx.) Torr. were grown for 48 hours in darkness at constant temperatures of 22°, 27°, 32°, or 37°C either in distilled water or polyethylene glycol 20,000 (PEG) solutions with osmotic potentials of −3.2, −7.7, and −9.8 bars. Redicle growth rate decreased as concentrations of polyethylene glycol increased. Radicle growth was reduced at 32° and negligible at 37° for L. multiflorum. All levels of PEG-induced osmotic stress reduced radicle growth at 22° and 32°, while at 27° only higher levels reduced growth of L. multiflorum. PEG-induced osmotic stress reduced radicle growth of B. curtipendula significantly at all temperatures except 37°, where the lowest level of PEG had an insignificant effect on radicle growth. With L. stipulacea, low levels of PEG-induced osmotic stress did not have a significant effect on radicle growth, but an osmotic stress of −9 bars reduced growth at all temperatures.
Calcium adsorption on the root exchange sites of 4 vegetables as determined by the isotopic exchange method (Ca40–Ca45) was a function of its concentration in the external solution surrounding the roots. As the Ca concentration was increased over the range 0.2 me–8.0 me Ca/1, there was an increase in the Ca adsorbed on roots of sweet corn, cv. ‘Gold Rush’, garden bean cv. ‘Topcrop’, lettuce cv. ‘Bibb’ and cabbage. The Ca adsorption curve of all 4 vegetables showed a plateau between concentrations of 1 and 2 me Ca/1. Root CEC values obtained at Ca concentrations corresponding to this plateau compare closely with values reported by other methods, and are more representative of established CEC values than those reported where the Ca concentration in the external solution was 0.5 me Ca/1.
An examination of dormancy in seeds of Eastern Redbud, Cercis canadensis L., showed that dormancy is controlled by permeability of the testa. Scarification by H2SO4 or mechanical abrasion permitted rapid and complete germination of dormant seed. Stratification was necessary only if seed were not scarified. Nonscarified seeds showed almost no water uptake during 55 days at 5°C, while scarified seeds had a steep imbibitional gradient. Germination was not stimulated by adding oxygen. No growth inhibitors were detected in dormant seed, and no promoters were found in chilled seeds.
Both physical and metabolic events were found important in the dormancy-regulating mechanism of seed of Elaeagnus umbellata Thunb. Covering structures offered mechanical resistance to germination, but they did not restrict the flow of water to the embryo. Oxygen concentrations from 60 to 100% increased germination, indicating that the endocarp and seed coat may restrict gaseous exchange by the dormant embryo. Restricted gaseous exchange may compliment a germination-inhibiting substance found in dormant seed. Gibberellic acid decreased the stratification period, but kinetin and potassium nitrate were ineffective.
C2H2-reduction activity of excised root nodules of 9 woody species was studied to determine the N2- fixation capabilities at various temperatures. Nodules of nonlegumes [Alnus glutinosa (L.) Gaertn., A. rugosa (Du Roi) Spreng., Comptonia peregrina (L.) Coult., Elaeagnus angustifolia L., E. commutata Bernh., E. umbellata Thunb., and Shepherdia argentea Nutt.] had maximum C2H2-reduction rates near 30°C. Nodules of the nonlegume Hippophae rhamnoides L. and the legume Robinia pseudoacacia L. showed maximum activity at 20° and showed no significant change at 30°. The C2H2reduction activity of all species except E. angustifolia declined at 40°. High temperature injury (40°) was irreversible. Activity was very slight at temperatures near 0°. Arrhenius plots of the data indicate the reduction rate is biphasic with the change in activation energy occurring from 11° to 20° depending on species.