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 dee to the drying out of the media are common 
phenomena in old cultures 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 
syringe, and a third type produced by the olive 
tubercle organism. 
QUESTION OF 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 
may be regarded as the working tools of protoplasm. 
The following are some of the best known kinds: ~ 
(1.) 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, ete., must 
*Fic. 57.—Crystals formed in cultures of Bacterium syringae (van Hall). 1. 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.1 and 2drawn 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 1 month old, 4. e., made January 20, 1904; drawn February 17-19. x 3. ‘Tempera- 
ture during growth, 20° to 25° C. 
