YELLOW DISEASE OF HYACINTHS. 



(Synonyms: Wakker's Bacterial Disease; Yellow .Slime Dutch Geele Snot.) 



DEFINITION. 



This is a specific communicable disease of the common hyacinth, the most characteristic 

 sign of which is the appearance in the bulbs of a bright yellow bacterial slime (pi. 19). 

 On cross-sections of the bulb the disease appears in the earlier stages as small yellow dots, 

 and on the longitudinal section as long, narrow, yellow stripes, corresponding to the loca- 

 tion of the vascular bundles, which are the first parts to be conspicuously infected. In later 

 stages the parenchyma is involved, the bulbs are badly decayed, and there are then various 

 secondary infections (see plate 20, figs. 7, 11). Other signs are dwarfing and one-sided 

 growth of the foliage, and water-soaked or brown stripes on the leaves. 



HOST-PLANTS. 



This disease is known to occur only in the common Dutch hyacinth (Hyacinthus 

 oricntalis). It has been successfully inoculated into this species. The leaves of the 

 inoculated plants showed the characteristic stripes and at the end of some months unmis- 

 takable signs also developed in the interior of many of the bulbs. It has also been inoculated 

 by the writer into the leaves of Hyacinthus albulus, Allium cepa, and Amaryllis atamasco, 

 but only with slight local results ; in no case did the bulbs of these plants become affected. 

 No results were obtained from inoculation into the leaves of cabbage. 



GEOGRAPHICAL DISTRIBUTION. 



So far as known the disease occurs only in the Netherlands, where the hyacinth is 

 grown in vast gardens for export to all parts of the world. 



SIGNS OF THE DISEASE. 



The first sign in an inoculated leaf consists of stripes having a water-soaked appearance 

 (plate 19, figs. 1 to 3). These are soon followed by the yellowing, browning and death of 

 the tissue first attacked and by the appearance of water-soaked spots or stripes farther down, 

 which in turn die and dry out. vSometimes the killed tissue becomes more or less trans- 

 parent except the veins, which are feebly browned. In natural infections, these stripes 

 usually begin toward the apex of the leaf. They extend downward rather slowly, but 

 much more rapidly in this direction than sidewise. The result is that often the leaf will 

 come to have a central dead stripe extending nearly or quite its whole length, while the 

 margins of the leaf are still green and healthy in appearance. Sometimes the bulbs are 

 infected from the flower-stalk. The signs in the scape lower down may or may not be 

 external. When externally visible there is a water-soaked appearance (plate 19, fig. 4 and 

 plate 20, fig. 5), followed by browning and shriveling. The signs in the bulb are so striking 

 as to be unmistakable. In early stages of bulb-infection the disease is confined quite 

 strictly to the vascular bundles, from one to fifty or more of these being yellow and full of 

 bacterial slime, in a white and otherwise healthy tissue (fig. 131, and plate 1 9, fig. 8) . When the 

 infection occurs through leaves, the scales which bear these particular leaves are the first 

 part of the bulb to show the yellow slime, and naturally this appears first at the top of the 

 scale in the vascular bundles. A little later the bacterial slime from these particular scales 

 grows down into the solid base of the bulb (the plateau) where many of the numerous 



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