HORTICULTURE. 237 



Origin of the banana, P. B. Popenoe (Jour. Heredity, 5 (1914), No. 6, pp. 

 273-280, figs. 2). — A jwpiilar review of the literature of the subject, including 

 reference to vagaries of pollination and irregularities in the behavior of the 

 banana under cultivation. 



Relation of bacterial transformations of soil nitrogen to nutrition of 

 citrus plants, K. F. Ivellerman and R. C. Wbigut ( XJ. S. Dept. A)gr., Jour. Agr. 

 Research. 2 (1914), No. 2, pp. 101-113, figs. 7). — The present paper comprises a 

 contribution to the knowledge of decadence in citrus trees, with special refer- 

 ence to citrus malnutrition, chlorosis, or mottle leaf. 



An examination of the soluble-salt content of soil samples taken throughout 

 southern California confirmed the results of other investigators in showing a 

 wide variation in the percentage of carbonates, chlorids, nitrates, and sul- 

 phates. Diagrams are given showing the relative nitrogen-fixing power, nitrify- 

 ing power, and salt content of soil samples taken from good and poor areas in 

 a productive orange grove and in unproductive and chlorotic orange groves. 

 These data indicate that when adjacent areas are compared the soils from the 

 vicinity of deteriorating trees are richer in nitrate nitrogen. The quantities 

 of other salts show no constant relationship to good or poor areas. The nitrate 

 content of poor areas was not excessive except during irrigation, at which 

 time the shallow lateral roots are exjiosed to a solution which is temporarily 

 stronger than during the intermediate periods. Extensive greenhouse experi- 

 ments with grapefruit and sour-orange seedlings growing in greenhouse soil 

 and in California soil at Washington, I). C, here described, indicate that 

 nitrate nitrogen in excess produces the typical symptoms of malnutrition. 

 These results ar£ corroborated by reports that in some cases applications of 

 fertilizers high in nitrogen to orange groves showing symptoms of malnutri- 

 tion have accelerated instead of retarded the deterioration. 



The experiments indicate that nitrates are more toxic than chlorids, that 

 nitrates and chlorids together intensify the symptoms of injury, and that 

 moderate quantities of lime — less than 10 per cent of calcium carbonate — exert 

 a more or less pronounced protective action. The range of toxic limits for 

 nitrates in the pot experiments is given as between 0.05 and O.Ol per cent as 

 compared with 0.005 to 0.015 per cent in the field, exclusive of crusts. 



Although records are available which show at least temporary benefit from 

 the application of nitrate fertilizers to chlorotic orange groves, it would appear 

 that this benefit may be due to the previously excessive depletion of nitrate 

 nitrogen through the denitrifying action of substances such as mature straw 

 turned under to maintain the humus. The authors' greenhouse experiments 

 show that seedling citrus plants were actually forced by the addition of cellu- 

 lose and of straw into an apparently typical state of malnutrition through 

 nitrogen starvation caused by the unbalancing of the soil flora and the utiliza- 

 tion of all of the nitrate by the organisms which decompose straw and cellulose. 

 Green manures, on the other hand, while causing some actual loss of total 

 nitrogen do not materially disturb the ratios of the nitrogenous compounds. 



The evidence tends to show that the total nitrogen content of the soil is 

 of less importance than the control of the rate of nitrification. In pot experi- 

 ments a normal rate of nitrification .was secured with a green crop turned 

 under, hence this practice is recommended for maintaining the humus supply 

 of the soil. The experiments indicate that the extensive use of mature straw 

 is to be avoided, though light applications of straw to fields too high in nitrate, 

 probably also with the liberal use of ground limestone, might be advantageous. 



A bibliography of cited literature is appended. 



Eremocitrus, a new genus of hardy, drought-resistant citrus fruits from 

 Australia, W. T. Swingle (U. S. Dept. Agr., Jour. Agr. Research, 2 (1914), 



