16 



BACTERIA IN RELATION TO PLANT DISEASES. 



interior of the leaf-sheaths is rusty brown and covered with the sticky bacterial slime, 

 which is also sometimes seen oozing from other portions of the leaf. This slime oozes from 

 the stomata (figs. 5, 6, 7). In very bad cases the leaf-sheaths above the terminal bud are 

 completely stuck together, so that the growing shoot can not elongate naturally, but is 

 forced to bend on itself repeatedly and push out sidewise through the sheaths (figs. 8, 9). 

 The gumming together and pressure of the outer leaves around the terminal bud result 

 in the doubling, twisting, and bulging of the main axis and eventually the stopping of the 

 terminal growth. In the most pronounced cases the terminal shoot enveloped in its wrap- 

 pings has a club-shaped appearance. In such cases there is sometimes a development of 

 lateral shoots (figs. 10, 11) and of aerial roots. 



A very interesting sign, also mentioned by Tryon in his paper, is that of the red bundles. 

 We have heard much about red bundles in connection with the "Sereh" disease of sugar- 

 cane in Java, and, indeed, this reddening has been known as a subordinate (oxidation) 



phenomenon in many diseases of the 

 sugar-cane, but never has the writer 

 seen it more beautifully developed 

 than in canes inoculated with pure 

 cultures of Bacterium vascularum. 

 In all the "common green" canes, 

 diseased as a result of these inocu- 

 lations, many red bundles were 

 present (see plates 1, fig. 4, and 11, 

 fig. 1). It was a very striking sign 

 of the infection and could be ascribed 

 to no other cause. The writer re- 

 gards it as a reaction on the part 

 of the plant. According to Prinsen 

 Geerlings, there exists in the cellu- 

 lose of the normal sugar-cane a neu- 

 tral, colorless substance, not easily 

 soluble, which becomes yellow in 

 an alkali but changes to red and 

 finally to brown when brought into 

 contact with air. The nature of 

 this substance is unknown. In the 

 majority of these red bundles bac- 

 teria were no longer to be seen: In 

 place of them was a red formless mass (figs. 12, 13). Red and yellow bundles were inter- 

 mingled in the stems, however, and often the same bundle would be both red and yellow, 

 i. e., variegated, the yellow parts being filled with bacteria, c. g., lower part of fig. 12. 

 The same phenomenon has been observed in maize inoculated with Bacterium stewarti, 

 except that in the latter case the variegated bundles were yellow and brown. The red 

 pigment was most pronounced in the nodes and immediately under them (fig. 11). This 

 was observed in many canes. Without exception there was more pigment in the upper 

 part of the internode than in the central or basal portion, but by far the greater part was 

 in the nodes, where often nearly all of the bundles were as red as blood. Probably this 

 localized pigmentation is due to greater aeration through the leaf-traces centering in and 

 immediately under the nodes. f In the sugar-cane, as in the sweet corn, the pigment does 



Fig. 6.* 



*Fig. 6. A detail from fig. .s at X, showing the bacteria multiplying in the intercellular spaces and pushing toward 

 the inner surface of the leaf sheath, i. c, in the direction of the arrow, st, stoma. 



fWcnt has shown that the leaf-traces take a downward direction soon after entering the node. 



