COBB S DISEASE OF SUGAR-CANE. 



25 



in pure culture great numbers of the same yellow organism which had been isolated from 

 the Australian cane (fig. 1 7). The bacteria were present in very great numbers and usually 

 in pure culture in the yellow bundles of these stems. The extent of this stem infection 

 (resulting, be it remembered, from a few needle-pricks on leaf-blades several feet removed 

 from the nodes) will be better appreciated if transcripts are inserted from notes made at 

 the time the canes were cut. For this purpose some observations made at the end of the 

 third month will suffice. 



Brought in to-day (May 6, 1903) 4 sugar-cane plants, inoculated Feb. 6. They are all badly 

 diseased. Photographs were made of No. 6 (plate 2) and of Nos. 8 and 12 together (plate 3). 



No. 6. The height of this plant is about 70 inches to the curve of the top leaves. The height 

 to the youngest leaf is 40 inches, i. e., the plant is small for its age (6 months, nearly). Both of the 

 inoculated leaves are dead and dried, including the leaf-sheaths. Of the leaves lower down one is 

 dead and dry and has fallen off, and three others are partly dead that is, dead at the tips and along 

 one margin but green in the midrib and on the other margin. Farther up, three large leaves are 

 dead throughout, except the 

 sheath. Four others are dead 

 at the tips and in the case of 

 one for 4 feet downward. The 

 small terminal leaf is also dead 

 at the tip. The diameter of the 

 stem at the surface of the earth 

 is 0.68 inch. The diameter of 

 the stem a foot from the ground 

 is 1 inch, including the leaf- 

 sheaths. At the base of this 

 plant there are three young shoots 

 which are healthy in appearance, 

 and live buds in various stages 

 of pushing, one of them being an 

 inch long. Signs of disease in 

 the shape of bacterial slime are 

 present under the leaf-sheaths a 

 few inches from the base of the 

 stem, the inner surface being 

 gummy and wet. The inter- 

 nodes are short; the longest ones 

 are only about 2 inches in length, 

 but the surface of the lower in- 

 ternodes looks healthy. Gum- 

 ming of the inner surface of the 

 sheaths continues up a distance 

 of several feet, and on the inner 

 surface of one sheath the bacte- 

 ria are abundant enough to look 

 yellowish; the organisms have 

 also broken through from the interior of the stem in three places and come to the surface as yellow 

 slime on as many internodes. The sheaths are more or less rusty-brown spotted, especially in the 

 gummy parts on the inner surface. There is no indication of rottenness, but a considerable quantity 

 of gum covers the inner face of many of the leaf-sheaths, while the main axis is still green. Aphides 

 are not present. Most of this bacterial slime has come from the interior of the leaf-sheath, but some 

 from the interior of the stem. There is a tendency in this, just as in two other plants brought in 

 to-day, for the terminal bud to push out sidewise. In the interior of the plant above the terminal 

 bud there is much red-brown spotting of the tissues and much bacterial gumming. This rusty -red 

 spotting of the inner, rolled-up leaves those that are protected from the light and from surface 

 contaminations is very conspicuous. Terminal bud seems alive, but is crowded down on itself 

 (zigzag) by the drying up and gumming together of the sheaths above it. The base of the uppermost 

 young leaf is alive and wraps around another smaller leaf, the top of which is dead and gummy. 



Fig. 17. 



*Fig. 17. A pure agar culture of Bacterium vascularum poured from the interior of plant No. 9. 

 at 20 to 28 C. 



Age 8.5 days 



