YELLOW DISEASE OF HYACINTHS. 



337 



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, viz., 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 to 4 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, e. 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 



Fig. 132.* 



*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. 



