39 



SPORE FORMATION. 



No spores have been seen, and I am in considerable doubt as to 

 whetlier the spores observed in some of his cultures and studied so 

 carefidly by Dr. Wakker belonged to this species. He was never 

 able to find any in the host plant, and those which appeared in his 

 tubes may have been due to the fact that he was working at times 

 with contaminated cultures. None of his successful infections with 

 sporiferous material were made with spore masses entirel}^ free from 

 vegetative rods, and the latter are long-lived. This supposition of 

 mixed cultures is the more likely because his work was done at a 

 time when it was impossible to decide with ease and certainty on the 

 purity of any given culture — i. e., before the era of poured plates — 

 and especially because some of his gelatin cultures were certainly 

 contaminated, i. e., yielded gas bubbles. (See Fermentation tube 

 experiments described in Bulletin No. 28 dealing with the cultural 

 characters of this organism.) While, therefore, not wishing to deny 

 absolutely the existence of spores in this species, it seems to me that 

 further and more exact proof is necessary to demonstrate their occur- 

 rence. A great many old cxdtures, grown on a variety of media at 

 18° to 26° C, have been examined without finding any spores. None 

 were observed in the diseased bulbs, many of which were examined 

 with care. Neither did any spores form in cultures exposed for fif- 

 teen da3"s to air deprived of its oxygen by the potash-pyrogallic-acid 

 method (test by microscopic examination and by exposure for ten 

 minutes to 60° to 70° C. in alkaline beef broth). None developed in 

 solid or fluid cultures exposed six weeks in the thermostat at 34° to 

 35° C. These cultures included alkaline and acid beef broth and 

 cylinders of turnip and sugar beet standing in distilled water. Fur- 

 thermore, this germ will not grow at all or grows onlj' very feebly at 

 the temperature Avliich Dr. Wakker states to be most suitable for the 

 formation of the spores viz. 35° C. (See Maximum temperature for 

 growth, in Bulletin No. 2S.) Finally, no spores developed in cultures 

 which were first grown foi' a week or two at room temperatures and 

 then put into the thermostat at 34° to 35° C. Several different media 

 were tried, but vigorous growth stopped immediately, and after two 

 weeks all such cultures were dead. 



INVOLUTION FORMS. 



Some astonishing involution forms have been observed. They 

 formed a whitish i-inx at the surface of the fluid in strongly (soda) 

 alkaline beef-broth cultures to which 10 per cent cane sugar had been 

 added. The color was so pale that at fii-st the tubes wei-e su])posed to 

 be contaminated. Wheu examined mici-oscopically the cultures were 

 five weeks old. These bodies wei-e so immensi-ly swollen, fused, 

 twisted, and irregular in outline that seen on the slide no one to wliom 

 1 showed them liad any suspicion tliat they were bacteria. Involution 

 forms were also seen on old tui-nip and banana cultures. 



