356 Journal of Agricultural Research voi. xv.no. 6 



the other chambers all the potatoes remained sound. While the results 

 show some success at low temperatures from inoculating sweet potatoes 

 with Penicillium sp., this fungus, even when removed from the competi- 

 tion of other organisms, must for the most part be considered a sap- 

 .rophyte. 



Penicillium sp. forms blue masses of spores on the interior and on the 

 surface of the sweet potato (PI. 27, C). 



BOTRYTIS CINEREA 



Botryiis cinerea Pers. was often isolated from sweet potatoes, as well 

 as dasheens and other vegetables held at low temperatures. So commonly 

 was B. cinerea isolated that the writers suspected it to be parasitic under 

 the same conditions that several of the other fungi already discussed 

 were found to be storage-rot producers. 



Preliminary experiments were made first with raw sweet-potato 

 blocks. It is not believed that the results from the use of raw sweet-potato 

 blocks give a final proof of the parasitism of any organism, but they do 

 give some indications of what may be expected when the potato itself 

 is inoculated and exposed to similar temperatures. The raw blocks were 

 cut and dropped into test tubes containing sweet-potato decoction, 

 made according to the method described on page 339. These blocks 

 were then inoculated with pure cultures of Botrytis cinerea and the tubes 

 divided into five lots. One lot was placed in each of chambers i (1.12° C), 

 2 (4.6° C), 3 (6.15° C), and 5 (9.4° C.) of the Altmann thermostat. This 

 experiment was conducted with B. cinerea from two distinct sources. One 

 strain (No. 3900) was isolated from sweet potatoes exposed to a tempera- 

 ture of 5° C. for several weeks and the other (No. 3940) from cabbage 

 held in cold storage (o°-i° C.) for several weeks. In 16 days after 

 inoculation all the plugs were rotted in all the chambers by both strains. 

 The fungus fruited in the tubes. Controls held for the same experiment 

 remained sound to the close of the experiment. 



The above results were verified by an experiment in which potatoes 

 were used, nine of which after inoculation (strain 3940) by the "well" 

 method were put in each of compartments i (2.4° C), 2 (3.56° C), 4 

 (7.5° C), 6 (13.9° C), 9 (20.9° C), and laboratory room. The results 

 showed that this organism would decay sweet potatoes over a considera- 

 bly wider range of temperatures than was the case with some of the other 

 organisms which are virulent only at low temperatures. In fact, the rot 

 did not progress as rapidly in the low temperatures as in temperatures a 

 little higher. In other words, it required 30 days to completely decay the 

 potatoes in chambers i and 2, while in chambers 4 and 6 the potatoes 

 were entirely rotted in 20 days. In chamber 9 only two were completely 

 rotted, and the remainder partially so in 23 days. In the laboratory 

 room one potato was completely rotted and six partially so in 23 days; 



