conspectus: extra vegetal h.abitat 35 



rot and tuber-rot of the potato and Bacterium tumefaciens, 

 causing crown gall, sometimes certainly live in the soil, and the 

 soundest plants when set in such soils, especially if wounded, 

 are liable to contract the disease, if they belong to susceptible 

 species. The root-nodule organism of Leguminosae, which I 

 have not considered here, also lives in many soils, as every 

 one knows. 



MORPHOLOGY AND CULTURAL CHARACTERS OF THE PARASITES 



Most of the plant bacteria are small or medium sized rod- 

 shaped organisms. They have rounded ends and are of variable 

 length but are seldom more than 1/z in diameter and sometimes 

 less than 0.5/1. Very few parasitic coccus forms are known; 

 in fact, none are very well established, but animal diseases due 

 to cocci occur and presumably there are such plant diseases. 

 Some of these bacteria are Gram positive, others are not; few, 

 if any, are acid fast. All takes stains, especially the basic 

 anilin dyes, but not all stain with the same dye equally well. 

 Most of the species are motile by means of flagella — polar or 

 peritrichiate; a few are non-motile, genus Aplanohacter.^ Some 

 develop conspicuous capsules, others do not. Few, if any, pro- 

 duce endospores. Under special conditions long filaments and 

 chains are frequent. Under abnormal conditions many be- 

 come club-shaped, y-shaped, or otherwise branched. Lohnis 

 believes {Jour. Agr. Research, Vol. 6, July 31, 1916, p. 675) 

 that all bacteria have an amorphous stage, but such is not my 

 belief. Grown pure on culture media in mass, they are either 

 yellow, pure white, or brownish or greenish from the liberation 

 of soluble pigments. Red or purple plant parasites are not 

 known. We formerly supposed that there were no green fluo- 

 rescent species capable of parasitism, but now several are 

 known: e.g., the organism causing the lilac blight of Holland 

 {Bacterium syringae [C. J. J. van Hall] EFS), with pure cultures of 

 which the writer was the first to obtain typical infections, at 

 Amsterdam in 1906 (garden of the Willy Commelin Scholten 

 Laboratory, courtesy of Johanna Westerdijk) and afterwards in 



1 Smith, Erwin F.: ''Bacteria in relation to plant diseases." Carnegie Inst. 

 Washington, Publ. 27, Vol. 1, p. 171, 1905; Ibid. 21, Vol. 3, pp. 155, 161, 1914. 



