May x6,1921 Respiration of Sweet Potato Storage-Rot Fungi 219 
regards the first of these, it is a well-recognized fact that most fungi 
prefer a slightly acid medium, and in some cases if the solution is not acid 
they make it so. Since this subject is to be discussed more in detail in 
another connection, suffice it to say here that, as with the concentration, 
it is probable that the degree of acidity of the original solution was not 
optimum for all the organisms. Kunstmann considered the question 
of mass inoculation of the culture by spores and found that it exercised 
very little influence on the rate of respiration. There is at present some 
difference of opinion as to the influence of light on the respiration of 
fungi. Kreusler ( 13 ) and Wehmer ( 22 ) deny the influence of light on 
growth and respiration, while Bonnier and Mangin (r) and Elfving ( 6 ) 
ascribe a retarding effect and Ziegenbein (24) a favorable influence on 
some flowering plants. Probably all fungi will grow in the dark. Jans¬ 
sens and Mertens (10) found that the red Torula is influenced by light and 
behaves like green plants, respiration being apparently more pronounced 
in the light than in the dark. The writers have also found that certain 
organisms fruit abundantly when exposed to moderately strong light but 
remain sterile if grown in the dark. In the writers' present experiments 
the fungi were exposed to light for only a short period of time each day, 
when the incubator was opened to adjust the apparatus or to examine 
the cultures. 
The temperature of 29 0 C. at which the organisms were grown probably 
does not represent the optimum for many, if it does for any of these fungi. 
The results of many investigators have shown that there is a wide range 
of optimum temperatures between different organisms, some thriving as 
well at 37 0 as others at 25 0 . In fact, there is considerable variation 
between species of the same genus. Brooks and Cooley (j) showed that 
the apple-rot fungi vary in their temperature requirements, and Edson 
and Shapovalov' (5) showed that certain potato-rot and wilt-producing 
organisms of the potato had different optimum and maximum tempera¬ 
tures for growth. The writers found, for example, that Rhizopus 
tritici grows better at 35 0 than at 29 0 and will make a good growth at 
40° or above. Some intermediate temperature, therefore, had to be 
employed which would permit all the organisms to make a good growth. 
Furthermore, the fact must not be overlooked that the rate of C0 2 
production is more or less correlated with the temperature at which the 
fungus is grown. Ziegenbein (24) found that the optimum temperature 
for respiration of different flowering plants varied from 35 0 to 45°, and 
Kunstmann ( 14 ) and Stoklasa (19) report a similar variation for fungi 
and beetroot, respectively. According to these investigators the maxi¬ 
mum rate of respiration correlates closely with the maximum tempera¬ 
ture for growth. When the maximum temperature for growth is 
reached, the rate of respiration declines rapidly. 
