INFECTION THROUGH STOMATA. 



6i 



the ordinary stomata (vol. I, figs. 74 and 75), the subject will be treated under this head, 

 although it is considered probable that the other form of infection also occurs. In any 

 event, the copious functioning of the water-pores must contribute very materially to the 

 certainty of stomatal infection. 



In 1902 the writer studied this disease on Long Island, where it is prevalent, and 

 brought back pure cultures, the earlier ones received from 

 Mr. Stewart having been allowed to die. The infections 

 were obtained with various subcultures made from these 

 original cultures. The plants were inoculated in the seed- 

 ling-stage, the material for infection being obtained from 

 cultures on slant agar. The inoculations were made by 

 placing a small quantity of the bacterial slime on the tips 

 of sweet-corn leaves which, were extruding drops of water 

 (vol. I, fig. 73). This was done in the afternoon, generally 

 toward sunset, the plants, which were in small pots, being 

 well watered and placed under the greenhouse bench to 

 protect from the bactericidal action of light. After a day 

 or two they were taken out of the shade and placed on 

 the bench. They grew rapidly, and after some weeks, 

 during which time they were repotted once or twice, they 

 were planted out on one of the Department of Agriculture 

 farms. They were well cultivated, experienced no setback 

 by being transplanted to the open, and those which were 

 not dwarfed by the early appearance of the disease grew 

 satisfactorily. The first signs of the disease were at the 

 tips of the inoculated leaves, and on some of the plants they 

 appeared within a week. The first cases — that is, plants 

 showing secondary or general signs appeared in about 3 

 weeks, but not many developed so soon, most appearing 

 after 9 weeks. Cases to the number of several hundred 

 continued to appear until frost put an end to the experi- 

 ment about 3 months from the time of planting. These 

 plants were several feet high when the general or constitu- 

 tional signs first appeared. A macroscopic examination: of 

 all of these cases and a microscopic examination of a con- 

 siderable number of them showed that the first parts of the 

 stem to be infected were the basal nodes, i. e., those which 

 gave rise to the inoculated leaves. The organism finally 

 occupied the vascular system quite fully, filling the bundles 

 in many cases from the base of the stem to the male inflo- 

 rescence, a distance of 3 to 4 feet, and also passing out into 

 the bundles of the large middle and upper leaves, but 

 usually not reaching the surface of any part of the plant, 

 so far as observed, except on the inner surface of certain 

 leaf-sheaths and on some of the inner husks of the ears 



(fig- 14)- 

 The spot disease of Delphinium (vol. I, fig. 127) is another malady in which infection 



takes place readily through the unbroken leaf-surface and stem-surface, i. e., through 



Fig. 14.* 



*FiG. 14. — -Inner husk of sweet corn, showing yellow spots and water-soaked areas in parenchyma, due to Bacter- 

 ium stswarti. In places also bacteria were oozing to inner surface. The bundles were occupied by the bacteria. From 

 U. S. Dept. of Agriculture farm on the Flats below the Washington monument. Plant inoculated in seedling stage. 

 Photographed Oct. 21, 1 902 . Movement of organisms was from young leaves downward into base of stem and thence 

 slowly upward through vascular bundles of stem into ear, over 2^4 months meanwhile having elapsed. Natural size. 



