YELLOW DISEASE OF HYACINTHS. $37 
The period of incubation in the writer’s experiments varied from 3 to 30 days depending 
on the amount of infectious material employed and on the susceptibility of the variety. 
All of his inoculations were through the leaves and floral organs, and always at a consider- 
able distance from the bulb. In all cases pure cultures were used for the inoculations which 
were made in various ways, v1z., by needle-punctures, by hypodermic injection, by placing 
drops of infectious fluid in the flowers, and by submerging the tips of leaves in fluid con- 
taining the living organism. The last method led to no very conclusive results but since the 
writer’s experiments were not numerous and yet gave some indications of ultimate success, 
they should be repeated with distinctly negative results before we are warranted in asserting 
that it is impossible to communicate the disease by way of the stomata. ‘The other three 
methods were each successful. 
A great many leaf-infections were obtained and forty of the inoculated plants also 
showed the characteristic signs in the 
bulbs at the end of 2 to4 months. From 
the interior of the bulbs which became 
diseased in this manner this same organ- 
ism was re-isolated on several different 
occasions and grown in pure cultures 
which again produced the typical disease 
when re-inoculated. All the several hun- 
dred control plants maintained by the 
writer continued free from this disease. 
There remains, therefore, no good ground 
for doubting the general correctness of the 
statements advanced by Wakker as to 
the cause of this disease. It is not only a 
genuine bacterial disease, but one of the 
most peculiar and interesting vascular 
diseases known to the writer. 
The natural methods of infection 
(except from mother-bulbs to daughter- 
bulbs) are not well understood. The 
disease is readily induced through wounds 
and it is likely that the knife of the gar- 
dener is responsible for a portion of the infections. Inasmuch, however, as in many of the 
plants the signs are said to begin on the leaves at a considerable distance from the ground 
some other explanation must be sought, at least for a portion of the infections. On several 
occasions the writer succeeded in producing the disease in the bulbs by putting drops of 
infectious fluid into the flowers (fig. 132). It is possible, therefore, that the disease may be 
disseminated both by leaf-eating and by nectar-sipping insects. Signs have not been 
observed in the roots. 
According to Wakker, wet weather greatly favors the progress of the disease, while 
sunshine and dry weather are unfavorable to it. This is true, also, of many other bacterial 
diseases, ¢. g., tobacco-wilt and pear-blight. 
VARIETAL RESISTANCE. 
Twenty-five years ago it was common observation, according to Dr. Wakker, that 
some varieties were very little subject to this disease in fields where other varieties were 
badly attacked. He seems to have had no doubt about the “predisposition”’ of certain 
*Fic. 132.—Cross-section of base of hyacinth bulb showing cavity in the bundle due to Bacterium hyacinthi. 
Plant No. 67 inoculated through the flowers. Slide 502 A-Ag. Drawn with Zeiss 16 mm. and 12 ocular. 
