COBB'S DISEASE OP SUGAR-CANE. 27 



On cutting open the stem of No. 12, red bundles were found to the extreme base. These are 

 mixed in with yellow ones, from which there is a distinct bacterial ooze. 



Slit the basal 4 inches longitudinally. Here again the stem shows a series of red cross-stripes 

 corresponding to the nodes. In the internodes some of the bundles are bright yellow, others are red, 

 and still others are mixed (mottled) red and yellow, and there are bacterial cavities. 



The red stain is evidently a later stage, just as the black stain is a later stage in sweet corn 

 attacked by Bacterium stewarti. 



No. 5. This plant is a little smaller than No. 12. All the basal leaves are dead. Both of the 

 inoculated leaves are dead, including the sheaths. The terminal leaf is flabby and all the other leaves 

 arc more or less diseased, being dead at the tips and with dead margins for a long distance down. 

 The base of the plant for a foot up inside the sheaths is very wet and gummy, just like the others. 

 These sheaths are rusty spotted. There is a peculiar smell to the disease not unlike that of some 

 bacterial cultures, but I am not able to define it any closer. The inner sheaths are green and some of 

 them are badly rusty spotted. The color of the spots is a brick red. 



Cut open the stem at the base; the vascular system is stained a reddish-brown. This reddish- 

 brown staining is very conspicuous. The terminal bud appears to be normal. The tissues in its 

 vicinity appear to be sound in places, diseased in others. 



Other plants in this series gave similar results. These were examined in April or 

 else later on, in May and June (plate 4). 



January 5, 1904, only one good ratoon cane has come up from the stools. In addition 

 there are two small canes and a shoot a foot high. The large cane is free from signs of 

 disease at the base, or nearly free. The little shoot is free. Had these stools been healthy 

 they would have given many tall shoots. 



SERIES II. 1903. 



Fourteen shoots of Louisiana cane, Variety No. 74, were inoculated February 9, 1903, 

 from two potato cultures n days old by making needle-pricks on two leaves of each plant, 

 as in case of the first series of inoculations. At the end of 5 weeks all showed local signs of 

 the disease and six of the shoots also developed constitutional signs, but on the most of 

 them these were not pronounced. 



The greater number of these plants proved very resistant, i. e., subsequently they grew 

 out of the disease, although they were somewhat dwarfed by it. At the date of inoculation 

 these canes were the most vigorous ones in the patch, but when they were cut out for exam- 

 ination, on July 20, the largest and best canes were the sixteen uninoculated ones. These 

 big canes were small and inferior at the time the others were inoculated. 



From the inoculated canes dwarfed cuttings, containing red vascular bundles, were saved 

 for planting, but no yellow slime was present in the bundles of these stems; at least none that 

 could be detected with the hand-lens, and only one reddish-yellow bundle was seen. 



SERIES III. 1903. 



Eight shoots of common purple cane planted in the greenhouse on November 15, 1002, 

 were inoculated with Bact. vascularum on May 4, 1903. The organism used for these 

 inoculations was from cultures 7 days old on potato cylinders kept at room-temperatures. 

 These were subcultures made from colonies on Petri-dish plate No. 9, poured April 16, 1903, 

 from plant No. n of the common green cane inoculated February 6, 1903. The plate was 

 absolutely a pure culture of Bact. vascularum. 



The inoculations were made by spreading three or four 3 mm. loops of the organism 

 over about 6 or 8 sq. cm. of leaf-surface, generally about a foot above the top of the leaf- 

 sheath, and then making about 100 to 150 needle-pricks through this area. After the pricks 

 were made, two or three more loops of the organism were rubbed over the pricked area. 

 Two leaves on each plant were inoculated. Leaves near the top of the plant were chosen 

 when possible. The canes were quite tall at this time averaging perhaps 6 feet, and many 

 of the leaves reached to the top of the greenhouse (10 ft.?). The inoculated areas were 

 protected from the sun for a day by cuffs of manila paper. Five checks were made. The 



