YELLOW DISEASE OP 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). In all 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- 

 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. 



*FiG. 136. Cross-section of 6 hyacinth bulbs from a field near Haarlem, showing advanced stages of the 

 yellow disease due to Bad. hyacinthi. Photographed by the writer in the summer of 1906. 



Fig. 136.* 



