78 BACTERIA IN RELATION TO PLANT DISEASES. 



The cellulose of mosses, selaginellas, hepatics, lycopods, and of the fronds of ferns also 

 resists. 



Van Tieghem (1884) observed that when bacterial decay attacked the cut ends of 

 plants immersed in water, it was not limited exactly to the part underwater, although it 

 did not make any great progress in the part above water. This led him to make inoculations 

 in various plants, using what he calls the spore-bearing Bacillus amylobacter. He inoculated 

 potato tubers by means of punctures and placed them in a thermostat at 35 C. Those 

 which received deep punctures gave the best results. There was bacterial growth, the 

 formation of gas, and finally the decay of the whole interior of the tuber. Similar results 

 were obtained with peas first soaked in water and then punctured so that the cotyledons 

 were injured. The grains of starch remained unaltered, but the cell-walls were broken down. 

 If the bacteria were simply placed under the teguments of the pea without injuring the 

 cotyledons or the embryo there was usually no result. He then tried inoculation of fleshy 

 plants, leaves of Crassulaceae (Escheveria, etc.) stems of Cactaceae (Cereus, Opuntia, etc.), 

 and the fruits of Cucurbitaceae (cucumbers, etc.). The leaves of Crassulaceae and the stems 

 of the Cactaceae exposed in a well-heated room gave no result, although frequently re- 

 inoculated, but rotted rapidly when plunged into oil after inoculation. The fruits of cucum- 

 ber and melon gave an entirely different result. There was a rapid development of the 

 bacteria and simultaneous destruction of the tissue. In a word, the same result as with 

 potato tubers. 



Van Tieghem also tried injecting these bacteria into various submerged aquatic plants 

 (Vallisneria, Helodea, Ceratophyllum) "but always without result. The plant remained 

 sound in all its parts." 



The first critical study was by Spieckermann (1902). The following paragraphs on the 

 mechanism of the entrance of bacteria into the plant are condensed from his Beitrag zur 

 Kenntnis der Bakteriellen Wundf aulniss der Kulturpflanzen (Landw. Jahrbiicher, 3 1 Bd., 

 pp. 163-174). The organism, which is a white, liquefying, Gram-positive, non-sporiferous 

 i -flagellate, milk-curdling, acid-forming, nitrate reducing Schizomycete capable of rotting 

 various kinds of vegetables, will be considered in its proper place under soft rots. 



The parasitism of the organism depends on its ability to dissolve the middle lamella and to produce 

 a poison which is deadly to the protoplasm. The solution of the middle lamella is brought about 

 by an enzym which is still present in the expressed juice of decayed plant parts after the death of 

 the bacteria. The dissolving power which this sap still possesses is destroyed by boiling. 



For isolating the enzym the expressed juice of decayed carrots, potatoes, and onions was used. 

 The vegetables to be inoculated were very carefully washed with sterile water, cut in two, and 

 streaked on the cut surface with a large number of bacteria from a 24-hour old agar culture. At the 

 end of 36 hours in a damp chamber the vegetables were completely soft-rotted. The decayed mass 

 was scraped out from the unchanged epidermis with a sterile spatula and mixed with an equal weight 

 of sterile water. The mixture was extraordinarily viscous. The carrot and onion mixture were 

 strained through a towel and then filtered through glass wool. The potato was centrifuged and 

 then filtered. The expressed sap obtained in this way was always very viscous and heavily clouded 

 with bacteria. The reaction to litmus was the same as that of the decayed mass itself, i. e., the potato 

 juice was neutral or alkaline, the onion juice acid, the carrot juice neutral or slightly acid. 



In order to do away with the action of the bacteria some of the solution was filtered through 

 a bougie, and to some of it disinfectants were added. The filtration through bougies failed entirely. 

 The filtrate free of bacteria no longer possessed in the slightest degree the dissolving power, while 

 the unfiltered solution showed this in the greatest degree until the close of the experiment. It must 

 be that the enzym can not pass through the bougie or at least only in a very dilute solution. For this 

 experiment 100 cc. bougies were used with Reichel's apparatus and 300 cc. of filtrate was obtained. 

 Since the action of the enzym, as will be shown later, is not essentially diminished by great dilution, 

 it is certain that the filtrate was completely enzym free. Potter and Laurent have been able to 

 filter through bougies the solution containing the enzym of their bacteria without impairing its 

 activity. It must here be noted that the slime present in the juice of the plant decayed by our 

 bacteria was also unable to pass through the bougie, so that the filtrate was no longer viscous. Per- 

 haps the collection of this slime on the outside of the bougie made it impossible for the enzym to pass 

 through. Neither is it possible even with very dilute juice to obtain active filtrate. 



