GEORGE K. K. LINK 593 



in most parts of the world, nevertheless bacterial diseases have been reported from 

 every continent, and are known to occur in flowering plants of 150 genera distributed 

 through more than 66 families. This list includes 3 diseases of gymnosperms and 23 of 

 monocotyledons, with the remainder distributed among the dicotyledons. A few bac- 

 terial diseases are known to occur among cryptogams. 



According to Smith, of Engler's list of 299 families of flowering plants, there still 

 are about 225 families of flowering plants for which no bacterial diseases have been 

 reported. Whether this is due to lack of investigators, time and chance, or natural 

 immunity remains to be determined. Smith lists a total of 155 described diseases for 

 66 families; but this does not represent the total of pathogens, because some of them 

 affect members of several families. In Bergey's Manual of Determinative Bacteriology^ 

 47 species of schizomycetes are listed as plant pathogens. This figure, however, does 

 not include all plant pathogens, for many cannot be included in a determinative 

 manual because of imperfect or non-differentiative descriptions. 



It appears at present that the families represented by a large proportion of cul- 

 tivated plants have a disproportionately large quota of bacterial diseases. Thus, the 

 families in which 5 or more bacterial diseases are reported are: Gramineae, 14; 

 Solanaceae, 10; Leguminosae, Rosaceae, and Crchidaceae, 7 each; Urticaceae, Cheno- 

 podiaceae, and Cruciferae, 5 each. Whether this is because the diseases of cultivated 

 forms are more completely known or whether there is a direct correlation between 

 abundance of diseases and growth of plants in culture is not known, and is a question 

 the answer to which lies in the future. 



CLASSIFICATION OF BACTERIAL PLANT PATHOGENS 



The schizomycetes which are phytopathologically significant belong with one ex- 

 ception to the Eubacteriales. This exception falls in the Actinomycetales {Actino- 

 myces scabies, cause of potato scab, which is characterized by proliferation of the 

 cortical tissues of the potato tuber). It wfll be of interest to await further work and 

 see whether all or most of the plant pathogens will fall, as they now do, into the family 

 Bacteriaceae, and whether grouping of these into the separate tribe Erwiniae on the 

 basis of plant pathogenicity will stand the test of time. It is not likely that animal 

 pathogens, with their high optimum temperature, will be found to be plant pathogens, 

 but there is a possibility that some of the plant pathogens with a high temperature 

 range might conceivably become pathogenic to animals. Smith^ reported the produc- 

 tion of small tumors in trout after inoculation with Bact. tumefaciens (the crown-gall 

 organism). Evidence of continual interest in studying the cross-inoculability of plant 

 and animal pathogens is found in a recent paper by Fygin, Epstein, and Funk,^ who 

 report the production of a plant tumor by a bacterium isolated from a human car- 

 cinoma. In the past, similar reports have not stood the test of more careful reinvesti- 

 gation. 



The classification and nomenclature used in Bergey's Manual have not been ac- 



' Berge}-, D. II. ,£/(//. ; Manual of Delerniinatiie Bacteriulogy. Baltimore: Williams & Wilkins, 1923. 



- Smith, E. F.: Bacterial Diseises of Plants. 



'Fygin, B., Epstein, T., and Funk, Casimir: "Sur une Tumeur vegetale provoque par une 

 Bacterie isolee d'un Carcinome humain," Coiiipt. rend. Soc. de bioL, 94 (14), 1097-9S. 1926. 



