STEWART'S DISEASE OF SWEET-CORN (MAIZE). 



131 



of toxic substances does not occur. Stewart's disease is preeminently a vascular disease, 

 but is not confined to the vessels exclusively, as he supposed. The disease, like many other 

 bacterial diseases, begins in the parenchyma and ends in the parenchyma. In the earliest 

 stages of the disease, in order to enter the vascular system the organism must first penetrate 



Fig. 58.* 



the epithem or multiply in the cellular tissues under the substomatic chamber (vol. I, 

 fig- 75) ! only in the rare event of infectious wounds made directly into the vessels can it 

 be otherwise. In the late stages of the disease, also, as already noted under "Etiology," 

 one very frequently finds conspicuous bacterial pockets in the soft parenchyma adjacent to 

 the bundles. The histological character of these pockets is 

 shown in figs. 48, 49. Their small size and their relative 

 abundance can be seen in fig. 53 and plate 9. The writer 

 has not observed in sweet corn any cavities at all compar- 

 able to the large ones frequently seen in sugar-cane attacked 

 by Cobb's disease. Many organs of the plant are subject 

 to invasion by this organism, i. c, roots, nodes, internodes, 

 leaf-sheaths, leaf-blades, male inflorescence, female inflores- 

 but there are no hyperplasias. Occasionally small 



cence ; 



\? s 





\ 





t> 



*w 



1 



F.g. 59. t 



shoots push from the base of the plant (plates 6, 8, 10), but 



these are not very numerous, nor frequent. In the ears 



the bacterial slime occurs in the cob, in the kernels (sparingly), 



and in the husks, often very abundantly in the latter, as may be seen by consulting my 



notes under "Etiology." From the husks the surface of the kernels is readily infected. 



*Fig. 58. A. A detail from fig. 57, at X, showing cavities in the vascular region of the outer layers of a corn 

 kernel occupied by Bacterium stewarti. Stained with methyl green and acid fuchsin. B. Similar infection, but from 

 another kernel and in cross-section. The slides prepared contain numerous serial sections and were numbered from the 

 base of the kernel upwards, 1, 2, 3, etc. The sections on slides 1 to 12 contain bacteria, i. e., to a point above the level 

 of the base of the radicle and close to the scutellum. Besides the central bacterial cavity, spiral vessels in the upper 

 part of the drawing are also sparingly occupied. The heavily shaded cells are part of the enveloping sclerenchyma. 

 Slide 485 A 1 (6, second row from top, second section from left, stained with pyronine and methyl violet. The bacteria 

 are deep red, the sclerenchyma is blue. 



fFiG. 59. A. Bacterium stewarti drawn unstained from the margin of a hanging drop. Organism grown in +15 

 bouillon for 52 hours. B. Bacterium stewarti from yellow slime on a potato culture 3 days old at 30 C. Rods motile, 

 many dividing. Drawn unstained from a hanging drop of water. 



