Which of the following lacks a nucleus on maturity ?

Options

A. Companion cells
B. Sieve tube elements
C. Phloem parenchyma
D. None of the above

Answer

To answer the question "Which of the following lacks a nucleus on maturity?" we need to analyze the options provided:

1. **Companion Cells**: These are specialized cells in the phloem that are closely associated with sieve tube elements. They retain their nucleus at maturity and play a crucial role in the functioning of sieve tube elements.

2. **Sieve Tube Elements**: These are the main conducting cells in the phloem. They are living cells but lack a nucleus at maturity. They rely on companion cells for metabolic support.

3. **Phloem Parenchyma**: These are also living cells found in the phloem and they do have a nucleus at maturity.

4. **None of the Above**: This option implies that all the previous options have a nucleus at maturity, which is not true as we have already identified that sieve tube elements lack a nucleus.

Now, let's summarize the findings:

- **Sieve Tube Elements**: Lack a nucleus at maturity.
- **Companion Cells**: Have a nucleus at maturity.
- **Phloem Parenchyma**: Have a nucleus at maturity.

Based on this analysis, the correct answer to the question is **Sieve Tube Elements**.

### Step-by-Step Solution:
1. Identify the cell types listed in the options.
2. Analyze the characteristics of each cell type regarding the presence of a nucleus at maturity.
3. Determine which cell type lacks a nucleus at maturity.
4. Conclude that the correct answer is **Sieve Tube Elements**.