62 



BACTERIA IN RELATION TO PLANT DISEASES. 



stomata. The disease has been obtained a number of times during the last seven years by 

 placing the bacteria in water and spraying this upon the plants. The leaf-serratures also 

 blacken in this disease, and here infection probably occurs through the groups of water 

 pores situated on their apex. 



The genuine bacterial spot of carnations is a fourth disease of this type. It was pro- 

 duced a number of times by Lloyd Tenny, one of my assistants, who kept the plants moist 

 under bell-jars for a day or two so as to get a deposit of water drops on the foliage, and then 

 sprayed upon the plants sterile water inoculated with pure cultures of the organism. Infec- 

 tions are visible within a few days. They always begin in the substomatic chamber, and 

 Petri-dish poured plates made from the interior of the spots on several different occasions 

 have yielded pure cultures of the parasite, which when reinoculated by spraying has again 

 produced the disease.* 



The spot disease of beans, caused by Bacterium phaseoli, is another example of stomatal 

 infection. Serial sections through very young spots demonstrated this to me beyond 

 reasonable doubt (fig. 15). Moreover, the disease was subsequently produced experimentally 



under my direction by Deane B. Swingle. 

 The spots appeared in large numbers in 

 about 6 days as the result of spraying 

 experiments and the earliest bacterial 

 nidus was in the substomatic chamber. 

 This manner of entrance explains, I be- 

 lieve, the fact once observed by Halsted 

 that nine-tenths of the spots in this dis- 

 ease were on the western side of the 

 pods that is, as I interpret the pheno- 

 menon, on those parts where rain drops 

 or dew drops would persist longest and 

 thus give most opportunity for infection. 

 The writer has observed the same thing 

 in connection with the black spot of the 

 plum. 



The spot disease of broom-corn also 

 arises by stomatal infection and has been 

 so produced by the writer, using pure 

 cultures but not of Bacillus sorghi. For early stages see figs. 16 and 17. 



The angular leaf-spot of cotton (vol. I, fig. 80) and the brown spot of Pelargoniums 

 are two other bacterial diseases in which infection commonly begins in the substomatic 

 chamber. The writer has studied both of these diseases in serial sections and has repro- 

 duced the first by simply spraying the bacteria upon the plants (fig. 18). The Pelargonium 

 leaf-spot was also so reproduced in 1906 by John R. Johnston, one of the assistants in my 

 laboratory, using pure cultures. 



Fig. 1 5.f 



*In honor of Albert F. Woods, the organism here in question, which is entirely distinct from Bacterium dianthi, 

 may be known as Bacterium woodsii n. sp. It is motile and non-sporiferous. It occurs as a short rod, single, paired, 

 or united into small clumps. Its growth is pearly white on potato and on agar, forming circular, small surface colonies 

 and spindle-shaped buried colonies on the latter. It blues litmus milk without separation of the casein (2 weeks). It 

 is non-liquefying and non-reducing (nitrates). Its maximum temperature for growth is about 35 C. It grows well in 

 beef-bouillon, potato-broth, and peptonized Uschinsky's solution, but not in Raulin's fluid. 



In early stages the spots somewhat resemble stigmonose but become unlike it as they enlarge. At first the spots 

 are water-soaked, then brown and sunken, somewhat resembling spots due to Septoria dianthi. As they enlarge the 

 spots are usually surrounded by a narrow water-soaked border. 



Habitat: Leaves, stems, and sepals of Dianthus caryophyllus, causing a spot disease. 



fFic 15. Cross-section of a bean-leaf attacked by Bacterium phaseoli. Natural infection, leaf collected in New 

 Jersey, aa, stomata; one cut cross-wise, other length-wise, bb, uninjured palisade tissue, chloroplasts shown in 

 outline only. The leaf has not yet entered into spot-stage nor have bacteria penetrated cells except perhaps at c, 

 which is heavily stained and appears to be a shriveled palisade cell occupied by bacteria. The infection undoubtedly 

 took place through the stomata. Slide 313 El. Drawn with a Zeiss 3 mm. apochromatic 1.40 n. a., No. 12 compensat- 

 ing ocular and Abbe camera. 



