90 BACTERIA IN RELATION TO PLANT DISEASES. 



was conspicuously whitened, i. e., bore prematurely dead and dry glumes. The same signs 

 appeared commonly in several kinds of sweet-corn grown in Washington in 1902 and inocu- 

 lated with pure cultures of this organism. Next in order of importance is the dwarfing of 

 the plant, which frequently does not reach half its ordinary size, and in some cases dies when 

 it is a few inches or only a foot or two in height. With the dwarfing there is a gradual dry- 

 ing out and death of the leaves one after another, from the base of the stem upward (plate 6) , 

 and with or without a previous conspicuous flabbiness of the foliage. The affected leaf, 

 without a preliminary yellowing, dies from the apex downward or from the margins in, 

 slowly or rapidly, according to circumstances, i. e., according to the amount of rainfall and 

 the more or less complete occlusion of those bundles below in the stem which supply it with 

 water. Young plants occasionally develop the disease very promptly, i. e., within a week 

 or two following primary infection, and such plants usually die a few days later. On the 

 other hand, infection may take place in the seedling stage and the appearance of the disease 

 be long delayed, i. e., until the plant is full grown, a period of 8 or 10 weeks intervening be- 

 tween the primary infection and signs of general collapse. In such plants, in the course of 

 some weeks following the appearance of secondary signs, all of the leaves dry out; but for a 

 short time the stem is still green and normal in its external appearance, and the roots are 

 white and sound on their surface. Later the stem dries out, and the roots brown and rot 

 with the appearance on them of various molds and bacteria. No conspicuous etiolation of 

 the leaves such as frequently occurs in sugar-cane attacked by Bacterium vascularum has 

 been observed in this disease, either on plants found diseased in the field on Long Island or 

 in those which became diseased in Washington as the result of pure-culture inoculations. 

 No marked proliferation from basal buds as in Sereh was observed, but in some cases there 

 seemed to be a slight tendency to push out shoots near the ground. 



If cross-sections are made of the green stems, i. e., before they begin to change color and 

 to shrivel, but after the male inflorescence has dried out and some of the leaves have shriveled, 

 a yellow slime will be seen to ooze from the ends of the bundles, usually from many bundles 

 and in great abundance (figs. 39, 40). In longitudinal sections of the stems the bundles 

 from which this slime oozes are observed to be bright yellow, the color being well set off by 

 the white parenchyma in which the bundles lie. Many internodes are usually occupied by 

 these yellow, slime-infested bundles, there being, however, nothing on the surface of the 

 stem to indicate their presence. The upper nodes may be either normal in appearance or 

 distinctly yellowed by the presence of the slime. The lower nodes, *'. e., those diseased for 

 the longest period, are always brown within and not infrequently, as one traces the signs 

 upward from node to node, there is a gradual transition from deep brown in the lowermost 

 nodes through pale brown and yellow to normal white or greenish-white at the top of the 

 stem.* Sometimes also the basal internodes are internally more or less browned, the paren- 

 chyma as well as the bundles, or only some of the latter. Browning of the internodal bundles 

 is not nearly as uniform and conspicuous as in cruciferous plants attacked by Bacterium 

 campestre, and is usually observed only toward the base of the stem in bundles presumably 

 long occupied, but sometimes appears higher and often appears prior to the death of the 

 stem. In the same internode a part of the bundles may be brown and the rest yellow. 

 There can be no doubt, I think, that this browning is due in some way to the presence of the 

 organism, but why some bundles brown and others do not, is not perfectly clear. It may be 



'Stewart had a different idea. He says: " The fact that the whole interior of the lower end of the stem is brown 

 signifies nothing. This browning is found in healthy plants as well as in diseased ones." In another place he says: 

 "The blackening of the fibro- vascular bundles, a not uncommon occurrence, is not due to the action of the corn bac- 

 terium." And again: " There is no disorganization or discoloration of any of the tissues." The writer has occasion- 

 ally found a brown stain in the basal nodes without distinct evidence of the yellow bacterium, on hasty examination 

 with the compound microscope, but the reverse of this he has never seen, viz, absence of brown stain in the basal nodes 

 when the bacteria have been abundant in the stem as the result of infection in the seedling stage. It is always there and 

 also often in nodes farther up the stem, as the reader will be convinced, I think, on reading what is said under Etiology. 

 The brown stain is not normal to the nodes of the maize plant, although, of course, it is a stain not restricted to this 

 one disease and may be a host reaction. 



