Nov. II, 1918 Sweet-Potato Storage-Rots 339 



The initial experiments consisted mainly in smearing spores from pure 

 cultures, or hyphae of the sterile fungi, on unwounded or on cut surfaces 

 of healthy potatoes. They were then placed in moist chambers with wet 

 filter paper in the bottom and under the lid and kept on a table in the 

 laboratory. Almost without exception the potatoes remained sound. 

 These preliminary experiments were repeated, but diflfered in that each 

 potato after inoculation was wrapped in moistened filter paper and then 

 in oiled paper. The results again were negative, a few being infected 

 with softrot but no more than in the controls. 



A considerable number of tests were made with the different organisms 

 by inoculating sterile cut blocks of raw sweet potatoes in test tubes with 

 a little water added. While the results so obtained were not entirely 

 satisfactory, they suggested the more promising rot-producing organisms. 

 Some of these inoculated tubes were placed in the various chambers of 

 the Altmann thermostat, the temperature of which ranged from nearly 

 zero to 40° C. It was shown thereby that temperature was one of the 

 controlling factors, and other experiments showed that humidity was 

 equally important with most organisms. The importance of humidity 

 suggested at this stage of the work that although the potatoes were in a 

 nearly saturated atmosphere in a moist chamber the spores were not 

 suspended in sufficient moisture to permit germination. It is a fact 

 easily recognized that moisture may condense on a damp chamber and 

 yet the potatoes remain dry. Evidently potatoes, as already reported 

 (iS),^ absorb the moisture from the surface, leaving the spores without 

 sufficient water in which to germinate. This difficulty was somewhat 

 overcome by pouring sterile water in wells about i cm. deep and about 

 I cm. in diameter made in the potato with a cork borer. Spores were 

 suspended in the water and the top sealed over with a cover slip set into 

 vaseline. It was hoped by this means to retain the moisture long enough 

 to allow the spores to germinate. This practice yielded better results 

 than any previously tried, but was by no means satisfactory or consistent, 

 the water being often absorbed before the spores had time to germinate. 

 In the belief that previously germinating the spores might be a solution 

 of the difficulty, a decoction from sweet-potato roots was made as follows : 

 500 gm. of sweet potatoes were finely cut into 1,000 cc. of distilled water, 

 the whole steamed for one hour, and then filtered through gauze. If 

 needed for immediate use, 2 cc. of this solution were put into test tubes 

 and autoclaved for 1 5 minutes at 1 1 pounds' pressure. Generally a con- 

 siderable quantity of stock solution was prepared for future use. This 

 was put into large flasks and steamed for 20 minutes on three consecutive 

 days. When needed, 2 cc. of this stock solution were transferred to test 

 tubes, which after autoclaving as above were inoculated with the spores 

 of the fungus under investigation. After about 24 hours, and rarely 



Reference is made by number (italic) to " Literature cited." p. 366-368. 



