20 



many colonies developed. The plates were usually pure cultures, or 

 almost pure cultures, of Fs. fluorescens, and two varieties of it were 

 recognized. This is a rod-shaped organism, and is one of the com- 

 monest microbes found in water and soil ; it is not usually associated 

 with plant diseases. Two varieties of the germ were recognized, one 

 from stems becoming brownish to amber in color in rotting, and the 

 other from stems showing a greenish-blue color in rotting. Both 

 varieties liquefy gelatin with green-yellow fluorescene. Some fresh 

 plants of celery were obtained, and the outer leaves were cut away. 

 The inner leaves were washed under the tap, and covered with mer- 

 curic chloride solution, one part to a thousand of water, then rinsed 

 in sterile water and each stem put into a large sterile test tube con- 

 tainina: a little sterile water in the bottom. In three weeks, four out 

 of fourteen stems so prepared showed signs of rotting, but some 

 remained sound after a month, and were then inoculated with pure 

 cultures originally isolated from the celery. Some of these stems in 

 test tubes had been standing in the sunshine and had regained their 

 green color. To inoculate them a sterile platinum needle was dipped 

 into the pure culture and thrust into the stem. After one day at 

 room temperature the rot was sometimes evident, and, in about four 

 days, juice from the rotting stem had accumulated in the bottom of 

 the test tube, and the stem was softened throughout so that it could 

 be shaken down into a soft pulp in the bottom of the test tube. 

 Plates from such inoculated and rotted stems developed colonies of 

 Ps. fluorescens in pure cultures. 



While tlie weather continued cold the celery in the cellar re- 

 mained sound, although it developed a sweet taste ; but, when warm 

 weather came in early spring, what had not been consumed, rotted. 



By such study we learn that bacteria cause decay, and that decay 

 takes place under conditions in some measures known to us and under 

 our control. To keep celery well it should be packed with the roots 

 in clean soil. For this purpose it is best to use the humus, or muck 

 soil, in which the celery is commonly grown. The soil in which the 

 roots are packed should be kept moist, but not wet, with good water. 

 The cellar or storage room should be kept at a uniform low tempera- 

 ture, a little above freezing. Free ventilation should be provided, 

 both as a means of regulating the temperature and for the health of 

 the plants. It should be remembered, also, that celery kept in a 

 close, foul atmosphere becomes tainted. 



