5 I 4 
Journal of Agricultural Research 
Vol. V, No. 12 
vidual experiments. The first experiment, however, is in marked con¬ 
trast to the others in this respect, for, although the sugar content of these 
sweet potatoes rose from 0.94 to 1.23 per cent, there was no corresponding 
rise in the respiration. The parallelism between the respiration and the 
sugar content is less marked when the different experiments are com¬ 
pared. Thus, the roots in the second experiment contained approxi¬ 
mately the same percentage of reducing sugar as those in the third, yet 
the respiration was much lower in the second. This fact, as has been 
pointed out, may probably be ascribed to the treatment to which the 
sweet potatoes had been subjected before the experiment. It is evident 
on the whole that the respiratory activity of the sweet potatoes is as 
greatly influenced by seasonal changes and environmental factors to 
which they have been exposed as by the sugar content. It is clear, of 
course, that with the exhaustion of the carbohydrates immediately 
utilized in respiration, the rate of respiration will fall, as in the case of 
seedlings grown continually in the dark, but it seems that an increase 
of the available carbohydrate supply does not necessarily entail a con¬ 
tinued increase in the respiratory activity. That there is sufficient sugar 
present in sweet potatoes, as well as in plant organs generally, to support 
a more active respiration than usually takes place, is shown by the 
increased respiration as a result of wounding. Table II gives the carbon- 
dioxid output per kilogram per hour of two lots of sweet potatoes for a 
short period before and after they were split lengthwise. 
Table II.— Carbon-dioxid output in milligrams per kilogram per hour of two lots of 
sweet potatoes for a short period before and after being split lengthwise 
Before roots were split. 
After roots were split. 
Days. 
Output 
of carbon 
dioxid at 
5 # C. 
Output 
of carbon 
dioxid at 
30 * C. 
Days. 
Output 
of carbon 
dioxid at 
5 *C. 
Output 
of carbon 
dioxid at 
30* C. 
T. 
Mgm . 
4.4 
4. I 
4 - 7 
5 - 4 
5 '1 
5 - 6 
Mgm . 
42. 7 
39- 2 
36.3 
35-4 
32. 8 
29. 8 
7. 
M gm . 
9-3 
6.9 
7.2 
7.2 
7-4 
7-3 
7.6 
Mgm . 
60. O 
So. 8 
52 . 7 
70. 7 (?) 
56.4 
54 - 5 
52 . 5 
2. 
8. 
7 . 
Q... 
A . 
IO. 
<. 
II. 
6 . 
12. 
13 . 
The great increase in respiration after the sixth day, when the roots 
were split, shows that there was sufficient sugar present to support a 
more energetic respiration than that which took place in the whole roots, 
but that other limiting factors than the sugar supply determined the 
rate of respiration. 
In the consideration of the question of the relative availability of the 
monosaccharids and the disaccharids as sources of material for respira- 
