Aug. i6. 1915 Nasturtium Wilt 453 



15 days complete wilt of several leaves occurred. The results were 

 checked under the microscope. For the most part the plants outgrew 

 the disease. Verbenas showed wilt within two weeks, and after three 

 weeks the tips, as well as the leaves, for 2 inches below the point of 

 inoculation, were completely wilted. Agar-poured plates from one of 

 these stems gave pure cultures of B. solanacearum. 



NATURAL METHODS OF INFECTION 



The organism may enter the nasturtium plant through wounded roots 

 or shoots or through the stomata. To demonstrate root infection, six 

 nasturtium seeds were planted in each of four pots. Two pots were 

 watered with a suspension from young agar cultures of the nasturtium 

 organism and then covered with fresh soil. The others were held as 

 checks. When the plants had four good leaves, the soil was worked in all 

 the pots deeply enough to break some roots. Six weeks later one plant 

 in an inoculated pot was badly wilted, and 10 days later four others 

 succumbed, while those in the check pots were perfectly healthy. One 

 week later all but 3 of the 12 plants in the inoculated pots had suc- 

 cumbed. Sections from stems of a number of these wilting plants were 

 examined under the microscope. The vessels were seen to be clogged 

 with bacteria, and there was the usual tissue disorganization. 



Before the organism was identified, spray experiments were started 

 to determine whether stomatal infections could be obtained. Well- 

 grown plants of both tall and dwarf varieties of nasturtiums were sprayed 

 in cages with a suspension from 3-day agar-slant cultures. Repeated 

 spraying with sterile water kept the plants moist for 30 hours, after 

 which they were removed from the cages. Six days later a few minute 

 brownish spots appeared on the leaves, but these did not enlarge mate- 

 rially. Four weeks later, however, one plant was characteristically wilted, 

 and within three weeks from this time all of the dwarf plants and one of 

 the tall ones had succumbed, with characteristic bacterial infection of 

 the vascular system. 



Another experiment was made with young plants, each bearing two 

 large leaves. They were sprayed in cages with suspensions from young 

 agar cultures and kept moist for 48 hours. Four days after the experi- 

 ment was started the large leaves all showed decided brown spotting 

 and water-soaked areas. The spots centered about the stomata in every 

 case examined, and often, but not always, they were marginal. After 

 two weeks the spots had coalesced in many places and appeared to be 

 affecting the small veins of the blade. Poured plates from such spots 

 gave typical colonies of B. solanacearum. Portions of the leaves in both 

 these stages were embedded, sectioned, and stained, and bacterial foci 

 found in the substomatic chamber, thus demonstrating stomatal infec- 

 tion. In the younger stages the bacteria appear in the stomatal open- 

 ing, as well as in the large chamber beneath (fig. i). In older stages the 



