YELLOW DISEASE OF HYACINTHS. 343 
yellow color so conspicuous in the attacked bundles. Often the xylem is the only part of 
the bundle attacked. When the vessels become thus occluded the walls give way, probably 
by solution, and the bacteria flood out into the surrounding parenchyma, which, however, 
is quite resistant. In the end, cavities are formed in the parenchyma surrounding the 
bundles, but the progress of the disease in this tissue is extremely slow. These cavities 
are filled with remnants of the vessels and cells of the host-plant and by enormous numbers 
of the yellow bacteria. In the formation of cavities in the parenchyma the intercellular 
spaces are first occupied (figs. 133,134,135). Inall of the diseased bulb-scales examined by 
the writer prior to 1906 the bulk of 
the tissues was still sound and the 
organisms were either confined to 
the bundles, or had made compara- 
tively small cavities around the 
same. In several hundred bulbs 
examined in Holland, in August, 
1906, the disease had made more 
extensive inroads (fig. 136) and 
large areas, especially of the inner 
face of the diseased scales, were 
yellow and gummy (plate 20, figs. 
8, 9, 10). The disease seems to 
progress a little more rapidly in the 
base of the bulb, where there is a 
net-work of vessels in rather close 
connection. Here also cavities are 
formed in the tissues. A small por- 
tion of the base of a bulb in an early 
stage of infection is shown in fig. 
132. In the end the whole plateau 
becomes yellow and gummy and the 
surface is ruptured, letting in vari- 
ous molds and bacteria. The writer 
has not attempted to cut many sec- 
tions of diseased leaves, but Wakker 
did so carefully, after fixing in ab- 
solute alcohol, and showed that here 
also the downward movement of the 
organism is through the spiral 
vessels of the xylem. The few I 
have cut and examined confirm 
Wakker’s view (see figs. 137, 138). 
In the end, the whole plant is de- Fig. 136.* 
stroyed, but, so far as the writer has 
observed, when the disease is uncomplicated, there is never anything resembling a soft white 
rot, such as that described by Heinz. In none of the many bulbs examined by the writer 
in 1897-1901 had the disease progressed far enough for the organism to break out of indi- 
vidual scales and pass sidewise into the open spaces between the scales, but this phenomenon 
was observed in Holland in 1906. 
Although the action on the cell-walls is slow, there can be little doubt I think that in 
the end the cell-wall proper as well as the middle lamella is dissolved and disappears. I 
have not established this fact, however, beyond dispute. 
*Fic. 136.—Cross-section of 6 hyacinth bulbs from a field near Haarlem, showing advanced stages of the 
yellow disease due to Bact. hyacinthi. Photographed by the writer in the summer of 1906. 
ec eg 
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SLES CTS NT 
