BACTERIA ON THE SURFACE OF PLANTS. 33 



Haven Mectalf found a non-pathogenic red Schizomycete associated almost constantly 

 with the Piricularia disease of rice in South Carolina. Its habitat is undoubtedly the surface 

 of the rice plant. 



In experimenting with peas Mrs. Bitting found that fresh peas taken from the pods 

 under sterile precautions always failed to contaminate culture-media, and that this condi- 

 tion of sterility persisted for a number of hours (fig. 2), but not for days. Peas from pods 

 picked for a longer time than 18 hours, often infected cultures and gave, with lapse of time, 

 an increasingly large number of contaminations, showing that the surface bacteria were 

 able to enter the unopened pods and contaminate the seeds (verbal communication). 



In his physiological experiments with germinating seeds of Vicia faba, etc., where 

 surface sterility was necessary, Harley H. Bartlett obtained it in many instances by care- 

 fully slipping the soaked seeds out of their seed coats. 



Diiggeli, in Zurich, studied this subject quantitatively as well as qualitatively. He 

 experimented with about 40 species of plants, some of which were sampled repeatedly. 

 He selected sound parts seeds, fruits, stems, leaves, and whole plants in case of certain 

 seedlings grown in sterile sand. A great many gelatin poured-plates were made, and his 

 detailed studies involved an enormous amount of labor. 



In general he found great numbers of bacteria on the surfaces of plants. Only very 

 exceptionally did he fail to obtain them, but occasionally they were few. Shaking the stem 

 or other part in water for ten minutes did not remove all of them. He therefore made his 

 comparative tests by grinding up a measured portion or weighed quantity of the material, 

 some of which then served for the test. 



The same organisms were found on seeds, seedlings, and mature plants. In general 

 there was a poverty of species. A few species occurred on so many plants and over and 

 over again so abundantly that he was forced to regard them not as accidental occurrences, 

 i.e., not as organisms which had settled down out of the air, but as true epiphytes peculiar 

 to the surface of the plants. 



The most common form was a motile gelatin-softening yellow schizomycete, named 

 by him Bacterium herbicola aureum, but said to be the same as the Bacillus mesentericus 

 aureus isolated by Winkler from the surface of plum leaves. This form occurred on a 

 great variety of plants, often to the exclusion of other species. For example, of 55 samples 

 of seeds examined, 21 bore this organism, practically to the exclusion of all others, while 

 only 7 samples were free from it. This organism is a short, actively motile, non-spor- 

 iferous rod, single or paired, i to 3 x 0.6 to o.y/x, forming characteristic zoologese. No 

 statement is made respecting number or attachment of flagella. It is gold-yellow on 

 gelatin and agar (gray at first), and gold-yellow on potato. Milk remained unchanged or 

 was curdled by acid, some acid formed also in the bouillon. Urea was not converted into 

 ammonia. Nitrates were reduced, and there was a strong indol reaction in bouillon 6 days 

 old. The organism is aerobic and probably facultative anaerobic. Growth was good the 

 whole length of the stab, but ordinarily no gas was formed from grape-sugar. It does not 

 stain by Gram. Growth and pigmentation on agar streaks was more rapid at 37 C. than 

 at 30 C. 



A second common form was a liquefying, green-fluorescent species, identified by him 

 as Bacillus fluorescent (Fliigge). A third species, Bacterium putidum (Fliigge) L. & N. 

 was also found widely distributed. According to Diiggeli these three species are the 

 dominating ones on the surfaces of plants. 



A fourth common species produces a manganese red pigment on potato. This is 

 called Bacterium herbicola rubrum. It was feebly motile and did not liquefy gelatin. Other 

 sorts were much less abundant. Of these he names: Bacillus mesentericus, B. vulgatus, 

 B. megaterium, and B. coli. 



