BUTLER: SUGAR IN TUBERS OF SOLANUM TUBEROSUM 113 
When potatoes containing sugar are placed at 20° C. respiration 
immediately increases to a very marked extent, while in the case 
of similar potatoes containing none or only traces of sugar the 
increase is very slight. The respiration of the potatoes con- 
taining sugar, while very rapid at first, reaches a maximum in one 
and a half or two days, and then gradually decreases until it 
becomes equal to that of potatoes containing little or no sugar. 
TEMPERATURE 20°C 
CARBON DIOXIDE RESPIRED 
IN PARTS PER MILLION 
U T T T T T T 
Se Bee Ie ee ee ee 
DURATION OF EXPERIMENT—IN DAYS 
Fic. 1. (After Miiller-Thurgau.) Respiration of potatoes containing different 
amounts of sugar at 20° C. Legend: : 
Respiration of 50 potatoes containing an average of 1.7814 per cent reducing 
sugar. : 
— — — — Respiration of 50 potatoes containing an average of 1.464 per cent reducing 
sugar 
------ Respiration of 50 potatoes containing none or only traces of reducing sugar. 
The results obtained by Miiller-Thurgau are very striking and 
are well illustrated in the above graph taken from his work. 
(FIG. 1.) 
It is perfectly obvious that the respiratory activity of potatoes 
foie 
ez 
% 3297 
wo 
@ei5+ 
We 0°G. 
xe 107 
ag Oo ero te 
z n : 
Sg 0 : . 
Be . ¢ Ss fh. Be Oe See 2 ee ee ee ee 
s~ DURATION OF EXPERIMENT—IN DAYS 
Fic. 2. (After Miiller-Thurgau.) Influence of change of temperature on res- 
piratory activity of potatoes initially rich in reducing sugar. 
is more influenced by the presence of sugar than by temperature. 
Sugar is essentially a limiting factor. This is well illustrated in 
the second graph (FIG. 2), in which the respiratory activity of 
