230 EXPERIMENT STATION RECORD. 



for Pseudomonas alone, 2.30 mg. of nitrogen ; and for the two combined, 4.51 

 mg. of nitrogen. 



Cultures of tliese bacteria under soil conditions were obtained by inoculating 

 limed and sterilized garden soil with pure cultures of both Azotobacter and 

 Pseudomonas, and then incubating for 21 days at 24°. Five grams of this 

 infected soil in 100 cc. of water (plus 1 gm. of glucose) was then incubated 

 for 24 hours and used as inoculating material for a series of tests on limed 

 and unllmed garden soil contained in pots. At the end of an incubation period 

 of 10 days at 24°, the pots inoculated with the mixed cultures of Azotobacter 

 and Pseudomonas showed an increase in nitrogen, both in the limed (35 mg. 

 per gram of soil) and the unlimed (25 mg. per gram of soil), over the unin- 

 oculated soil, amounting in the limed soil to nearly 350 lbs. per acre for a 

 depth of 4 in. 



The results of experiments now in progress on the utilization by higher 

 plants of this fixed nitrogen will be given in a future paper. 



On growth stimuli, A. J. Nabokich {Bot. Centbl., Beiheftc, 26 (1910), 1. Abt., 

 No. 1, pp. 7-lJi9, charts 6). — The results are reported of investigations on the 

 secondary action of water, on the action of a vacuum, and S'Pfthe influence of 

 bases, salts (especially halogen compounds), and oxygen on plant growth. 



It is claimed that resting cells and mature parts of plants with a reduced 

 metabolic assimilation are able to remain for a long time without injury in 

 an oxygen-free atmosphere, but that, on the contrary, young growing cells 

 in the absence of oxygen soon succumb, with the typical symptoms of the 

 poisoning of the protoplasm resulting from certain metabolic assimilation 

 products. The more vigorously the plants manifest their capacity for growth 

 and for metamorphism of organic substances, the more energetically the poison- 

 ing occurs. 



Air, howevei", with its normal gas content seems to be an unfavorable medium 

 for the growth of young plants. The growth occurs energetically in rarefied 

 atmospheres, in gas mixtures containing small amounts of oxygen, and in 

 water in which insignificant quantities of air are dissolved. The dampening 

 of plants by means of sprays or guttation accelerates their growth. It seems 

 that oxygen acts as a strong chemical reagent by exerting a stimulating influ- 

 ence on the protoplasm. Weak concentration of oxygen materially increased 

 the activity of the protoplasm and therefore the growth of the tissues, while 

 appreciable quantities of this gas checked cell activity, thei-eby hindering and 

 stopping their growth. 



From the experiments it seems certain that the action of alkalis, acids, and 

 salts on plants is caused by the specific influence on the protoplasm of the ions 

 found in the solution. The cations and anions of most compounds have 

 been shown to produce effects opposite in character. The anions produce a 

 strong acceleration while the cations hinder or limit growth. 



The growth effects of the sa't solution were found to be the average result 

 of the opposite acting ions. In most cases the cations in the solution are 

 dominant, and therefore determine the resulting effects on plant growth of a 

 given salt. 



The eflfects of radium rays on plants, C. Acqua (Ann. Bot. [Rome], 8 

 {1910), No. 2, pp. 223-23S) .—The results are given of the effects of radium 

 rays on the germination of seeds, development of seedlings, carbon assimilation, 

 growth of polien tubes, and movements of protoplasm in several green plants. 



It was found that a great difference in the reaction to radium rays existed 

 between different species, and even between different organs of the same species. 

 The root system in general responded to the action of radium, where a more or 

 less complete arrest of development was shown, although many exceptions 



