No abstract

Nitrogen fixation (acetylene reduction) was found to be associated with sand erain root sheaths (rhizoshcalhs) occurring on the following xeric grasses: Oryzopsis hymcnoiilcs (Rocm. and Shult.) Ricker, Agropyron dasyslachyum (Hook.) Scrib., Stipa comata Trin. and Rupr., and Aristidu purpurva Nutt. Acetylene reduction rates associated with whole plant specimens of these species varied from 515 to 920 nmol C^H^Ag dry wt.) x (6 days). Nitrogeniisc activity was shown to be associated with the rhizo sheaths. Bacillus potymyxa\\)/ic nitrogen fixers were isolated from the rhizosheaths of each grass. The isolates reduced acetylene and assimilated "N,.

The factors affecting the hatching of mosquito eggs have been studied by several investigators. Atkin and Bacot ('17) found that the eggs of Aedes aegypti (L.) (Stegomyia fasciata, A. calopus) rarely hatched in sterile fluids, but that they hatched readily when living bacteria or yeasts were added. Killed cultures of bacteria and watery extracts of yeasts caused only a small percentage of hatch, and no hatch was obtained with sterile filtered extracts of bacteria. Roubaud and Colas-Belcour ( '27) found that large numbers of eggs of this species hatched in concentrated filtered extracts of Escherichia coli (Bacillus coli) and yeasts. These investigators also found sterile solutions of pepsin, trypsin, and papain to cause hatching. Barber ( 'as), on the other hand, found that the eggs "hatched out in the water or in clear sterile media as promptly as in contaminated cultures," Hinman ( '30) had no difficulty in hatching the eggs of this species in the sterile filtrate from a tub of water in which larvae were developing.The discrepancy in these findings was investigated by Rozeboom ( '34).He found that less than 2% of the eggs of Aedes aegypti hatched in sterile water when they were allowed to dry before being immersed, but of eggs from 24 to 72 hours old that had not been allowed to dry, 51%) hatched in sterile water and 82% in solutions contaminated with bacteria. He concluded that the differences in hatching "may have been due to differences in the age and degree of drying of the eggs they used." On the other hand, Rozeboom found that hatches of the eggs of Culex pipiens, "C. territans," and C. salinarius were slightly larger in sterile water than in contaminated water. Mail (

Summary. When paraquat was added to four different soils, nitrification was not appreciably affected but ammonification of soil organic‐matter nitrogen was slightly retarded. Carbon dioxide evolution as well as oxygen consumption was used as an index of metabolic activity of soil micro‐organisms and paraquat had a stimulatory effect at higher concentrations. Oxidation of added sulphur was slightly depressed. Paraquat decreased both the total mould and bacterial populations in Chehalis silt loam. After 30 days incubation the percentages of Streptomyces and Penicillia were markedly increased by most treatments but were little affected in Chehalis silt clay and Woodburn soils. Except for the temporary suppression of nitrification, paraquat had no significant influence on general microbial activities of importance to soil fertility. Some bimodal effects or toxicity inversions were observed with intermediate concentrations. Effet du paraquat sur les activités microbiennes dans les sols