Fusariiim in Tuber Rot and Wilt of Potato 
27 
II. Ecology and physiology of the organisms 
METHOD AND DATA 
1. Temperature relations. — Observations of cultures grown 
at ordinary temperatures showed that there is a striking difference 
in the rate of growth of the two organisms. Potato cyhnder, rice, 
Hquid potato, and glucose media, and glucose and potato agar cul- 
tures all showed that F. oxysporiim makes a considerably greater 
initial growth at temperatures above 20° C. than does F. trichotheci- 
oidcs. At temperatures in the vicinity of 10-15° C, however, 
F. trichothccioidcs makes the greater initial growth, although these 
temperatures lie below its optimum. The same difference was noted 
in cultures on neutral and acid potato agar. This point was also 
tested with cultures on sterile slabs of potato tubers kept in Petri 
dishes. At 25° C, F. oxysporiim covered such slabs completely 
when F. trichothccioidcs barely had made a start, while at 12^ C. 
the situation was reversed. 
\\'hen 1 per cent liquid glucose media were inoculated with spore 
suspensions of F. oxysporiim, visible growth was made in 16 hours; 
when F. trichothccioidcs was used, 30-4-2 hours elapsed befors visible 
growth was made. This holds for temperature above 20° C. The 
optimum temperature for F. oxysporum was about 30° C, and for 
F. trichothccioidcs about 20-22° C, both varying slightly with the 
medium used. The maximum for F. oxysporiim lay between 38 and 
40° C. The optima and maxima were higher for cultures in potato 
extract than for glucose media cultures. The writer has not been 
able to determine the minima accurately because of inadequate 
apparatus. Humphrey (15) gives 4° C. as the minimum growth 
temperature for a certain strain of F . oxysporum. 
Potato agar cultures of F. oxysporum and F. trichothccioidcs 
could endure a temperature of 40° C. for 5 and for 20 hours respec- 
tively and remain viable. Exposure to 50° C. for 5 hours killed 
F. trichothecioides, but not F. oxysporum ; while exposure for 20 
hours killed both. Some F. oxysporum cultures survived 5 hours 
exposure at 57° C. 
The growth relations were also checked up quantitatively. 
In these experiments, as well as in all the following ones, the method 
