336 



BACTERIA IN RELATION TO PLANT DISEASES. 



anastomosing vascular bundles become yellowed, and where we often find a considerable 

 area of the intervening parenchyma yellow and soggy (plate 19, figs. 6, 7). Subsequently 

 the yellow slime extends upward into the bundles of other scales and sidewise slowly into 

 the parenchyma, until finally the bulb is destroyed. In the later stages of the disease 

 small pockets occur in the bulb-scales (plate 20, figs. 8, 9) and other bacteria frequently 

 enter and help to complete the destruction of the bulbs but their presence is not essential. 



In this stage, mites (Rhizoglyphus 

 hyacinthi) may also be present 

 (plate 20, fig. 7). Certain fungi 

 are also met with in later stages, 

 and notably a species of Penicil- 

 lium. This is extremely common 

 (plate 20, fig. 1 1 ) . Wakker states 

 that there may be also an up- 

 striping of the green leaves due 

 to their infection from the bulb. 

 The above signs progress very 

 slowly, several months to a year 

 being necessary, as a rule, for the 

 complete destruction of the bulbs. 

 Not infrequently the disease ex- 

 tends from the mother-bulb, by 

 way of the plateau, into daughter- 

 bulbs (Wakker, Smith). In such 

 cases the daughter-bulb always 

 shows the disease first in the basal 

 portion (plateau), and of course, 

 on the side next to the mother- 

 bulb. Bulbs are frequently at- 

 tacked on one side more than on 

 the other (plate 19, fig. 9), and this may result in a curved growth of the foliage which 

 bends over toward the diseased side. 



ETIOLOGY. 



. The cause of this disease is Bacterium hyacinthi Wakker; a bright-yellow, medium- 

 sized rod with rounded ends, motile by means of one polar flagellum, and multiplying by 

 fission. It is this organism which causes the yellow color in the bundles of the diseased 

 bulbs. The yellow slime in the bulbs is made up entirely of a homogeneous-looking bac- 

 terial growth which in early stages ordinarily yields pure cultures of this organism when 

 cultivated out with any degree of care, but which is sometimes mixed with other organisms, 

 especially in advanced stages of the disease. Wakker, who first studied this disease criti- 

 cally, obtained at different times a number of good cases as the result of wounds made in the 

 leaves, scapes and bulbs, but inasmuch as most of his successful inoculations were what the 

 writer has designated direct infections, i.e., the inoculation of raw material, there has been 

 a tendency on the part of various writers to discount his results, and to confuse the general 

 reader by speculations not based on any experimental data. Dr. Wakker's statements are, 

 however, in the main, trustworthy, since the writer has obtained numerous successful con- 

 firmatory inoculations from pure cultures of this yellow organism (for figures consult 

 Bulletin 26). 



Fig. 131. 



*Fic. 131. Early stage in the destruction of a hyacinth bulb by Bad. hyacinthi. Cross-section of bulb enlarged 

 to show diseased vascular bundles in 3 scales. These 6 bundles were bright yellow. A seventh bundle, which does 

 not show plainly in the cut, was also diseased. Several of the dark spots are negligible, being shadows due to slight 

 openings between the scales. Plant inoculated Feb. 16, 1897, on upper part of scape. Photographed June 23, 

 1897. Circa x 3. 



