26 BACTERIA IN RELATION TO PLANT DISEASES. 



up into the inner tube and from this transferred to the culture-medium. At the same time 

 sterile bouillon was put on the crushed tissues, thus giving two series of cultures. The 

 culture-medium was sterilized veal bouillon. Numerous experiments led di Vestea to the 

 following conclusions: 



(i) Cultures made from plants which he gathered himself or which were brought to 

 the laboratory (Lab. de la Clinique Cantani, Naples) fresh from the country remained 

 regularly sterile whether in vacuo or exposed to the air. 



(2) If the same vegetables were left exposed to the air for a day or more, a new sample 

 very often gave positive results. 



(3) Finally, whenever the author worked with vegetables brought in from the market 

 he always obtained fertile cultures. 



"This last result is to be explained, I believe," says di Vestea, "especially by the fact 

 that the gardeners and produce dealers water their vegetables, to keep them fresh, with 

 water which is usually swarming with bacteria." 



In 1888, Dr. Bernheim claimed to find bacteria in the interior of seeds of cereals, but 

 Lehmann, in whose laboratory he had worked, discredited his views, stating that Bernheim's 

 studies were very incomplete researches made under direction and published during a vaca- 

 tion period without his teacher's knowledge or consent. 



The same year in discussing Bernheim's paper Dr. Buchner says that he (Buchner) 

 obtained negative results from histestsof normal vegetable tissue for the presence of bacteria. 



In 1889, Dr. Lehmann, discussing Bernheim's work said: "Normal plant seeds are 

 germ-free." In 43 gelatin-roll-cultures made out of at least 800 fragments from the interior 

 of beans, chestnuts, maize, peas, and almonds, he obtained only 6 bacterial colonies, which 

 undoubtedly came from the air. At the conclusion of his paper in the Archiv fur Hygiene 

 he says: "I summarize the second part of my work thus: That Buchner certainly is right 

 in considering Dr. Bernheim's pellicles for non-living formations but that in opposition 

 to Buchner's view they did not consist of fat, but of salts." 



Laurent experimenting on several occasions with various plants, viz., seeds of barley, 

 maize, and lupin, tubers of potato, bulbs of onions, roots of carrot and chicory, and the 

 fleshy tissues of Cereus, Agave, and Carica, obtained the same results as Fernbach. The 

 interior of these plant parts was found to be free from bacteria. 



In 1890, Laurent showed that the sap flowing from the cut surface of healthy vine- 

 stems contains no bacteria, i. c, none of these organisms were taken up by the roots. 

 Eleven tests were made on as many young potted grape-vines, placed for a few weeks in 

 winter in a hothouse. In each case the shoot was flamed, cut, the cut end renamed, and 

 then plunged into a tube plugged with cotton and containing 10 cc. of sterile veal broth. 

 In 24 hours, 5 to 10 cc. of sap had oozed out and mingled with the culture-fluid. The 

 branches were then removed and the tubes incubated at 30 C. In a week's time only 1 

 tube developed bacteria. Some of the fluids were neutral, others were slightly acid, and 

 the rest were slightly alkaline. 



In 1 89 1, Kramer found no bacteria in the interior of sound potato-tubers (for a long 

 review in English see American Naturalist, 1897, pp. 123-138). 



In 1892, Russell reached the same conclusion respecting several plants. 



In more recent years Hiltner has reached the same conclusion respecting the interior 

 of sound seeds. He found the tissues of those he tested always free from bacteria. 



The writer has sometimes found bacteria in fleshy roots supposed to be normal, and 

 the surface of which had been properly sterilized, but these had been dug for some time. 

 The parenchyma of healthy plants is always or almost always free from bacteria. Prob- 

 ably the vascular system, especially of some parts of the roots, frequently contains bacteria, 

 and certainly they must be present to some extent in those plants in which tyloses are 

 abundant, if the latter are due to the stimulus of bacterial products as believed by the 

 writer (see fig. 30 and page 91). 



