Step 1: Interest on debentures.
Debenture holders receive a fixed interest, irrespective of profits earned by the company.
Step 2: Nature.
This interest is treated as an expense of the company and must be paid before arriving at net profit.
Step 3: Conclude.
Therefore, interest on debentures is a charge against profit, not an appropriation of profit.
Final Answer:
\[
\boxed{\text{A charge against the profit of the company}}
\]