Notes on Recent Literature. 
for several hours the respiration at ordinary temperatures is 
increased; it reaches a maximum intensity about the second day 
and then slowly falls to the normal intensity. The full effect was 
found to depend upon a sufficiently long exposure, and not upon the 
variation of the temperature in heating and cooling. With higher 
temperatures the maximum intensity was higher and was reached 
rather later ; and after exposure to 44" the normal intensity was 
not regained, but a permanent increase in the rate of respiration 
resulted. 
It is an interesting fact that no stimulation was observed 
except with temperatures of 38° and over. The effect appears to 
be such that beyond a certain minimal temperature (37" for one 
sort of potato) the amount by which the maximum rate of respiration 
reached by the heated tubers exceeds the rate of respiration of 
similar unheated tubers is closely proportional to the difference 
between the temperature used and the minimal temperature, at 
which the stimulation is zero. Thus after 44" the respiration curve 
showed a rise 2^ times as great as after 40". This appears to be 
true regardless of the original intensity of the respiration which 
differed considerably in tubers containing different percentages of 
sugar. (The increase in the total amount of C0 2 evolved, the total 
amount of “ stimulus-C0 2 ,” will of course not be proportional to 
the rise above the minimum temperature, but will be much greater 
for each succeeding degree). 
From a study of the sugar changes produced, the authors 
conclude that the fundamental effect of the heating is a weakening 
of the protoplasm like that ensuing normally as the age of the 
tuber increases. As a result of this the storage of starch by the 
leucoplasts, one of the higher protoplasmic activities of the cell, 
suffers greatly, while at the same time even the lower, enzymic 
processes, the inversion of cane sugar and the dissolution of starch, 
are appreciably retarded. Thus at 18"C heated potatoes retain a 
considerable percentage of sugar in their tissues; while at 0", at 
which temperature starch-formation is largely inhibited even in 
normal potatoes, the slower formation of sugar shows that heating 
has acted injuriously on that process also, though to a less degree. 
The parallel investigation of changes in sugar-content and 
respiratory activity involved the halving of the tubers, as the only 
method of ensuring similarity in all respects between control and 
experimental material. The results were then, however, complicated 
by the additional reaction to injury. Under these conditions it was 
found that the two effects were antagonistic. Under the weakening 
influence of a high temperature, reaction to wounding was at first 
inhibited, and even after the effect of heating wore off, the respiration 
never reached the same maximum intensity as was shown hy 
unheated pieces. On the other hand, while unheated injured tuber 
showed a permanent increase in the rate of respiration, weight for 
weight, in comparison with whole potatoes, the permanent increase 
was much greater in the case of the heated tubers. 
This permanent increase, observed with whole potatoes also, is 
attributed by the authors to increased sugar content. In order to 
feel quite sure that this is a sufficient explanation, one would like 
to have the results of a series of experiments with different 
temperatures, corresponding with their series for whole potatoes 
