66 BACTERIA IN RELATION TO PLANT DISEASES. 



also occurs frequently when the flowers, green fruits, or foliage are killed by other 

 causes. In the leaves of Amaryllis atamasco the writer obtained red stripes by 

 injecting the yellow Bacterium hyacinthi, but no bacterial disease followed, and the 

 same plant reddens when bruised. Broomcorn shows conspicuous red blotches 

 when attacked by the broomcorn organism, but the parasite itself does not produce 

 a red pigment, while the plant reddens easily as the result of aphis-punctures or 

 wounds of any sort. Sugar-cane attacked by Bacterium vascularum shows a con- 

 spicuous red stain in the bundles, but other causes, such as the gnawings of an insect 

 or the presence of a fungus, may lead to a similar stain, while the bacterium itself 

 does not produce any red pigment. 



CRYSTALS. 



Determine the nature of the crystals observed in the various media. Many of 

 these are double ammonium salts; others result from the action of.trypsin on pro- 

 teids. Crystals which are not due to the drying out of the media are common 



phenomena in old ciiltures of many sorts, especially if 

 the media were not originally saturated with alkali 

 (soda or potash). Fig. 57 shows two types of crystals 

 formed in +15 nutrient agar by two green-fluores- 

 cent organisms received from van Hall as Pseudomonas 

 syringte, and a third type produced by the olive 

 tubercle organism. 



QUESTION OK EXISTENCE OF ENZYMES. 



The enzymes of English writers are the diastases 

 of Duclaux. They are chemical substances, the exact 

 composition of which has not been determined. They 

 Fig. 57.* may be regarded as the working tools of protoplasm. 



The following are some of the best known kinds : 



(i.) Diastasic (starch-destroying). (5.) Lab or rennet (casein-forming). 



(2.) Inverting (sugar-splitting). (6.) Lipase (fat-splitting). 



(3.) Cytohydrolytic (cellulose-dissolving.) (7.) Pectic (pectin-splitting). 



(4.) Proteolytic (peptonizing). (8.) Oxidases (oxidizing). 



Trypsin is common. Pepsin is not known to be produced by bacteria and 

 should be searched for. 



Many bacteria invert cane-sugar, but invertase is believed to be rare. This, 

 however, may be an ill-founded conclusion. The experiments of various animal 

 physiologists have shown that when cane-sugar is injected into the blood-stream it 

 is excreted unchanged, and according to Julius Sachs cane-sugar, inulin, etc., must 



*FiG. 57. Crystals formed in cultures of Bacterium syringae (van Hall). I. From tube II, 

 Aug. 14 (agar stock 693), from van Hall's II, i.e., his own isolation corresponding to a, fig. 56. 

 2. From tube I, Aug. 14 (stock 693), from van Hall's I, which is from Beyerinck's old isolation (see 

 b, fig. 56) X 3. Nos. i and 2 drawn Aug. 30, 1902. 3. Crystals formed on slant litmus-lactose agar 

 which was inoculated with the organism causing olive-knot. About one-half inch of slant in middle 

 part of culture i month old, i. e., made January 20, 1904; drawn February 17-19. X 3- Tempera- 

 ture during growth, 20 to 25 C. 



