9 8 



BACTERIA IN RELATION TO PLANT DISEASES. 



ously. It was observed, however, on September 20, that many of the plants had begun to 

 show the staminate inflorescence. This was judged to be premature, since these plants were 

 only 2.5 feet high, i. e., they were plants dwarfed and prematured by the disease, but show- 

 ing as yet no other unmistakable signs. 



On October 7, cases began to appear again in the first series and then also for the first 

 time in the second series. For the sake of conclusiveness, even at the risk of being tedious, 

 the results of an examination of some of these cases will be described in detail, after which 

 the whole experiment will be summarized in a table. 



Record of the Diseased Plants. 



I. Photographed (plate 7, fig. i) and dissected. From vessels toward the base of the stem the 

 characteristic yellow slime oozed out. With proper caution two pure cultures were obtained on slant 

 agar by direct transfer; a third was contaminated by a green-fluorescent organism. 



II. No record. 



III. IV. Sep- 

 tember 8, photo- 

 graphed together 

 (plate 7, fig. 2). 

 Externally the 

 plants give no in- 

 dication as to the 

 cause of the disease. 

 The larger plant is 

 2 feet high without 

 stretching up the 

 leaves. The outer- 

 most four leaves 

 are shriveled and 

 brownish ; the upper 

 ones are wilted. 

 The smaller plant 

 is about 1 8 inches 

 high. All of its 

 leaves are shriveled 

 except the upper- 

 most one, which is 



wilted. The stem p- 42.* 



of the larger plant 



was cut off 6 inches from the roots. All the inner (undeveloped) 

 leaves are free from the organism, but the outer two or three are 

 infected. The same is true of the smaller plant. The bacteria 

 ooze out in the form of chrome yellow masses. Cut higher up, 

 the bacteria are less and less abundant, the infection of the 

 large leaves being clearly from the base upward. Cut within 

 i inch of the roots, the larger plant shows a pretty general infec- 

 tion of the vessels through all parts of the stem and a browning 

 of some of the bundles. The same is true of the smaller plant 

 except that at this level the browning is less conspicuous. The 

 basal i inch of the larger stem was then slit through lengthwise and inspected. The most badly 

 diseased part was the extreme base. Here there was much browning and some softening of the 



Fig. 43. t 



Fig. 444 



*Fic. 42. Radial longitudinal section through a maize stem (sweet-corn) attacked by Bacterium stewarti, show- 

 ing a badly diseased (browned) area in base of stem, '. e., in that part of the stem first occupied by the bacteria; also 

 browned vascular bundles in the internode, and sound exterior. Long Island, July 16, 1902. Compare with results of 

 pure-culture inoculations obtained in Washington and shown on plate 10. 



fFlG. 43. Bacterium stewarti stained 10 minutes in alkaline methylene blue and washed in water. A cover-glass 

 (smear) preparation made directly from the yellow ooze out of the stem-vessels of a sweet-corn plant collected on Long 

 Island, July 16, 1902. Figure made with Zeiss 2 mm. apochromatic 1.30 n. a. objective. No. 12 compensating ocular, 

 and Abbe camera, and drawing then reduced one-half. X 1,000. Compare with drawing made from slide stained with 

 carbol fuchsin. 



|Fic. 44. Cover glass (smear) preparation of Bacterium stewarti, direct from stem of Early Cory sweet corn. 

 Long Island, July 16, 1902. Stained 5 minutes in carbol-fuchsin. Staining irregular and wall often not well defined 

 (compare with vol. II, fig. 122, where a similar effect is visible). No spores. X 1,000. 



