cobb's disease op sugar-cane. 



23 



tip on the other side. The midrib is bright green the whole length. The needle-punctures were 

 made about a foot from the leaf-sheath. Secondary signs are visible on three of the upper leaves of 

 this plant as long yellowish stripes, interrupted in one of the leaves. In places on one leaf the stripe 

 is dead and reddish-brown for a distance of 8 inches and a breadth of one-sixteenth to one-eighth inch. 

 On another there is a marginal dead stripe 2 feet long. 



(3) Leaf j a is dead entirely from the tip down for a distance of 3 feet, and the rest of the way 

 it is dead on the margins, but the midrib is green. It was pricked about 18 inches from the top of 

 the leaf-sheath. The leaf-sheath itself is about a foot long. 



Leaf 3 b is dead at the tip and down for a distance of 3 feet and the midrib is dead a foot farther 

 down, but the margins are green. In the lowest foot both midrib and margins seem to be normal. 

 There are no secondary signs on this plant, which is 6 feet tall and bears 13 leaves. 



(4) Leaf 4 a is dead from the apex down a distance of about 3 feet, while for an additional 2 feet 

 it is dead on the margins but green in the midrib. Punctures made about 

 9 inches from leaf-sheath. Leaf-sheath is about 9 inches long. 



Leaf 4 b is dead from the apex down a distance of about 4 feet. A 

 foot farther down it joins the stem. The lowest foot of the leaf is dead 

 on both margins but green in the midrib. The plant itself is about 5 

 feet high and shows conspicuous secondary signs; 18 inches from the 

 ground the diameter of the stem, including the leaf-sheaths, is about half 

 an inch. It bears 12 leaves. Two of the upper leaves are dead almost 

 all the way down and two more show brown striping on one side. The 

 upper two are flabby. Plant brought in and photographed. It is the 

 larger of the two of this date. Bad. vase ul arum was plated from the stem 

 of this plant. A white gas-forming organism was also obtained from two 

 places in this stem, 8 inches apart. 



(5) This plant is about 4 feet high and is rather small. Diameter 

 of the stem a foot from the ground is a little more than 0.25 inch. Both 

 inoculated leaves are dried up throughout. The plant bears 10 leaves, 

 not counting some small basal ones which are dried out. It shows distinct 

 secondary signs, which consist of whitening and striping of the leaves. 



(6) Plant 6 is about 6 feet high. At a foot from the ground the 

 diameter of the stem is nearly an inch. It bears 14 leaves. Inoculated 

 leaf-blade 6 a, which is about 5 feet long, has dried out throughout, 

 except about a foot at the extreme base, and even here there are brown 

 spots on the margins running down to the leaf-sheath. The midrib, how- 

 ever, is bright green. 



Leaf-blade 6 b is dead throughout, except about 9 inches of the mid- 

 rib at the base. The sheath itself is also drying out. This plant shows 

 also conspicuous white, yellow, and brown striping on 3 of the upper 

 leaves (secondary signs). 



(7) Plant 7 is about 6 feet high. A foot from the ground the stem is 

 0.75 inch in diameter. It bears 13 leaves. Leaf 7 a, which is about 5 

 feet long (or 6 feet if the leaf-sheath be included), is dead throughout, 

 including everything except the base of the leaf -sheath. 



Leaf-blade y b, which is like y a in size, is also dead throughout, 

 including most of the leaf-sheath. There is distinct etiolation of the 

 margins of two of the uninoculated upper leaves, and there are also red 

 lines and specks in these etiolated parts for a distance of a foot in one leaf 

 near the base and a less distance on the other. 



(8) The diameter of the stem of this plant a foot from the ground is 

 about 0.625 inch. It bears 13 leaves. The check-leaf pricked on March 2 

 with more than 100 needle punctures at 6 inches from the stem, is bright green in the pricked area, 

 the only dead parts being the tissue immediately around the punctures, which is white. Leaf o' a, 

 which is about 4 feet long (5 feet with sheath), is dead throughout, except extreme base of sheath. 



Leaf-blade S b is dead for a distance of 4 feet down. The basal 1 foot is dead on the margin but 

 green in the midrib. There are distinct signs of secondary infection on the upper leaves which are 



Fig. 16.* 



*Fig. 16. Middle part of one of the uninoculated higher leaves of the common green cane, showing etiolation 

 due to secondary infection with Bacterium vascularum: Margins green and normal in appearance, midrib green. To 

 either side of the midrib are white stripes with red-brown dead spots and stripes in them. The white striping continued 

 to the apex of the leaf. In this stage of striping bacteria are usually present in some of the bundles of the affected 

 part of the leaf. Drawn from a broken negative. 



