172 BACTERIA IN RELATION TO PLANT DISEASES. 



"Let us take such an emulsion and add some drops of it to two tubes : one containing the normal 

 diastasic Hquid, the other the same quantity of this liquid boiled. They are put into the thermostat 

 at 38°. Of these two tubes, equally cloudy, the check after some hours remains cloudy, while the 

 other has become almost completely transparent." 



There is no precipitate and therefore the clearing can not be ascribed to agglutination. 



"Ainsi Dictyostelium mucoroides ne pent se developper qu'avecdes Bactdries; il est parasite des 

 colonies bacteriennes ; ses myxamibes ing^rent les Bacteries et les dig^rent dans leurs vacuoles k 

 I'aide d'une diastase dont Taction est assez semblable k celle de I'amibodiastase." 



Similar results were obtained with other species, i. e., Dicty. purpureum, and Polysphondylium 

 violaceum, showing that these also are bacterial parasites. 



These Acrasieae are strictly aerobic. As soon as a tube is sealed growth ceases. The amount 

 of humidity greatly influences the morphology of the sporophores. The optimum temperature for 

 growth is between 22° and 25°. Above 28° there is no development. They will grow at a tem- 

 perature as low as 8° but then very slowly. 



The morphology and the color of the Myxomycete are both changed by changes in the sub- 

 stratum, e. g., if Bacillus suhtilis is added to mixed cultures of Dictyostelium mucoroides and Bad. 

 fluorescens, the sporophores are longer and branched forms are frequent. 



Under some circumstances bacterial pigments are absorbed by the living Myxomycetes. The 

 author holds that certain Acrasieae described as distinct from Dicty. mucoroides on account of their 

 variation in color are only the same species associated with different chromogenic bacteria. These 

 bacterial pigments therefore have a taxonomic importance in the Acrasieae. Grown with Bact. 

 fluorescens the young fructifications of Dicty. mucoroides are fluorescent and the old ones are color of 

 a dead leaf ; grown with B. coli the fructifications of this species are pure white and remain so. When 

 Polysphondylium violaceum, which has a pigment of its own, is grown in the presence of Bacterium 

 violaceum its color becomes paler, the pigments of the two being chemically dissimilar bodies. 



Similar results as regards necessity for living bacteria were obtained with Didymium difforme 

 and D. effusum. 



So far as the writer has observed bacteria always occur in the club-root of crucifers 

 along with Plasmodiophora brassicae. 



One Bacterium with Another. 



This subject is a very large one and no attempt has been made to cover it either in 

 the text or bibliography. 



According to Beyerinck and Van Delden their Chroococcum assimilates nitrogen only 

 when it enters into symbiosis with other bacteria — Granulobacter , Aerohacter, etc. 



In 1906, Keding published his Weitere Untersuchungen. He found Azotobacter 

 not only on the surface of Fucus and several other salt water algae, but in dune sand near 

 the roots of strand plants, and in all investigated soils, except moor soil. Azotobacter 

 is able, he says, to assimilate the nitrogen of the air in pure culture, and this ability was 

 not increased by growing it in combination with other bacteria. The sea forms of the 

 organism can grow in the presence of 8 per cent salt. 



According to Bottomley "Pseudomonas radicicola and Azotobacter, together make a 

 powerful combination for the fixation of free nitrogen." These are both said to have been 

 isolated from the algal zone of the root- tubercles of cycads. He inoculated oats, barley, 

 hyacinths (galtonia), and parsnips with mixed cultures. Best results with oats which were 

 nearly doubled in weight. 



Thomas F. Manns (The Blade Blight of Oats; a bacterial disease. Agr. Exp. Sta., 

 Ohio, Bull. 210) has stated that a widely prevalent disease of oats is due to a symbiotic 

 relationship between two species of bacteria. 



