Nov. II. 1918 Sweet-Potato Storage-Rots 355 



(23° C), and an incubator the temperature of which averaged about 

 28° C, was twice repeated. In chambers 2 and 3, 70 per cent in the 

 one series and 90 per cent in the other were decayed. The sweet pota- 

 toes at all other temperatures remained sound. 



The results seem to indicate that Mucor racemosus produces a much 

 slower rot than Rhizopus nigricans, about two to three weeks being 

 required to complete the destruction of a sweet potato under optimum 

 conditions. The tissue is rendered a clajnsh white in spots, as shown in 

 cross section (PI. 27, A). It is somewhat wet, but spongy to firm. When 

 pulled apart or broken open, it pulls out in a fibrous, stringy manner. 

 It has a distinct starchy odor. 



ALrTERNARIA SP. 



Alternaria sp. is another fungus we have frequently isolated from sweet 

 potatoes held at low temperatures. Owing to its prevalence under such 

 conditions, inoculations were made by inserting spores and hyphae into 

 the end of some potatoes and exposing them to the temperature of cham- 

 bers 3 (7.19° C), 6 (i4.4°C.), 9 (2o.9°C.), II (26.o°C.), 16 (30.6°C.) of the 

 Altmann thermostat. Each sweet potato was wrapped in filter paper 

 and then in oiled paper. All the potatoes in chamber 3 were partially 

 rotted in 1 9 days. In chamber 6 only a slight rot had started and at the 

 higher temperatures all the potatoes remained sound to the close of the 

 experiment. 



Alternaria sp. produces a firm, moist rot. The tissue is first turned 

 brown and then gradually darkens, but never becomes black (PI. 27, B). 

 The potato breaks easily, and the parts separate without the formation 

 of strands so characteristic of soft rot. 



PENICILLIUM SP. 



The species of Penicillium which we most frequently isolated and -with. 

 which all our work has been done was given to Dr. Charles Thorn, of the 

 Bureau of Chemistry, for identification. According to his determination 

 it belongs to the expansum group, and is similar to a number of other 

 strains for which there are no specific differences. It was a common in- 

 habitant of decayed sweet potatoes and generally of those that were 

 decayed by other fungi. Occasionally it was isolated alone in pure culture, 

 but more often it was accompanied with one or more other organisms. 

 Like some of the other fungi already discussed, it was most often obtained 

 from potatoes held at low temperatures. That it may be, under a pro- 

 tected environment, a storage-rot producing organism at low tempera- 

 tures was demonstrated by a series of experiments in which chambers 2 

 (4.44° C), 5 (12.0° C), 8 (18.7° C), 10 (22.9° C), 12 (26.9° C), and 17 

 (32.0° C.) of the Altmann thermostat were used. In chambers 2 and 5 

 the potatoes were from one-fourth to two-thirds decayed in 39 days.. In 



