22 



BACTERIA IN RELATION TO PLANT DISEASES. 



made on each leaf, some in the midrib, but the majority in the tissue on either side of it. 

 The pricked area covered about 4 sq. cm. Three subcultures from as many separate yellow 

 colonies on the plates poured from the Australian cane were used. Many leaves were 

 pricked as checks, but these never developed any disease. Until nightfall the inoculated 

 leaves were protected from the light by paper, but the air was not shut off. A semitropical 

 temperature was maintained in the greenhouse and the plants grew rapidly, an important 

 factor. Three weeks after the bacteria were introduced by the needle-pricks the inoculated 

 leaves showed white stripes, in which reddish or brown dead spots and stripes soon appeared. 

 These stripes had their beginning in the inoculated part of the leaf and slowly spread upward 

 and downward. For some weeks there were no further signs of infection; then white 

 stripes appeared on other leaves (uninoculated ones on the same shoots) and, somewhat 

 later, the red or brown stripes, with shriveling of the leaf-parenchyma. At this time the 

 plants were considerably dwarfed, and this nanism finally became very marked (fig. 15). 

 The condition of these plants at the end of two months (April 3) was as follows: 



(i) The leaf / b is dead from the punctures down to the stem on each side of the midrib. The 

 distance from the pricked area to the top of the sheath is 19 inches. The length of the sheath itself 



is about i foot. The leaf is dried out on the 

 margins and brown above the pricked area for a 

 distance of 2.5 feet. The terminal one foot of 

 the leaf is bright green, and the midrib is green 

 throughout its whole length. 



The signs on leaf i a, which is about the 

 same length as the other, are the same, namely, 

 dry brown margins about 0.25 inch or more in 

 width extending down to the sheath and upward 

 to within a foot of the tip. The only marked 

 difference in the upper end is that the extreme 

 tip has lost its chlorophyl and a portion of the 

 leaf inside of the dry brown margins is also 

 yellow. The midrib is green throughout. The 

 yellow bacterial gum is oozing out of the green 

 midrib about 9 inches above the top of the 

 sheath, i. e., from the pricked portion. Two or 

 three little, bright yellow gummy masses are 

 present on the inner face of the leaf at this point. 

 This leaf was severed from the stem 3 inches 

 above the sheath. Photograph made. The 

 stem of the plant 1.5 feet from the ground is 

 about an inch in diameter. It has 17 leaves 

 and the height of the plant is about 7 feet. The 

 secondary signs of the disease are conspicuous 

 on most of the upper leaves. They have ap- 

 peared as white or yellowish-white longitudinal 

 stripes, which in some cases have already be- 



I 



Fig. 15.' 



come reddish-brown, not unlike the signs I 

 obtained some years ago by inoculating Bad. 

 hyacinthi into amaryllis leaves. They extend 

 in many cases from the base of the leaf-blade, 



in some instances half-way up, and in others entirely to the apex. This striping shows on five of the 

 upper leaves. One of the most conspicuously striped leaves was cut off and photographed (fig. 16). 



(2) This plant is about 6 feet high and bears 13 leaves. The check-leaf is normal ; that is, only 

 the tissues in the immediate vicinity of the punctures have turned white. The tissue in the pricked 

 area as a whole is bright green and normal in appearance. This is the plant from which a pricked 

 (inoculated) leaf was cut off some weeks ago and found to contain the organism. That leaf (the 

 foot-long stub) now has dry-shriveled nearly to the sheath. This is 2 a. 



The other inoculated leaf (2 b) is dried out and has become brown on the margins from the 

 pricked area down to the sheath and up to within 1.5 feet of the tip on one side, and entirely to the 



*FlG. 15. Row of inoculated badly dwarfed sugar-cane (at X) with a row of taller, sound, uninoculated cane 

 of same age to either side. Hot-house, Washington, D. C., 1903. Drawn from a broken negative. 



