The reason for successful establishment on land by seed plants is

Options

A. evolution of siphonogamy
B. development of secondary growth
C. presence of true conducting tissue
D. all of the above

Answer

To answer the question about the reason for the successful establishment of seed plants on land, we can break down the options provided and analyze each one:

1. **Evolution of Siponogamy**:
- Siponogamy refers to a type of fertilization that involves the formation of a pollen tube. This adaptation allows for the transfer of male gametes (sperm) to the female ovule without the need for water, which is essential for fertilization in many non-seed plants. This adaptation is crucial for seed plants as it enables them to reproduce effectively in terrestrial environments where water may not be readily available.

2. **Development of Secondary Growth**:
- Secondary growth is the increase in thickness or girth of a plant, primarily due to the activity of the cambium. This growth allows seed plants to develop a robust structure, supporting larger sizes and enabling them to compete effectively for sunlight and resources. This is particularly important in terrestrial habitats where competition for light is fierce.

3. **Presence of Few Conducting Tissues**:
- This option seems to be misleading. Seed plants actually have a well-developed vascular system, which includes xylem and phloem. This system is crucial for the efficient transport of water, nutrients, and food throughout the plant, allowing them to thrive in various terrestrial environments.

4. **All of the Above**:
- Given that the first two options (siponogamy and secondary growth) are significant reasons for the successful establishment of seed plants on land, and considering that the third option is not entirely accurate, we can conclude that the correct answer is not "all of the above" as it implies that all statements are correct.

**Conclusion**: The successful establishment of seed plants on land is primarily due to the evolution of siponogamy and the development of secondary growth. Therefore, the best answer would be a combination of the first two options, but since "all of the above" is provided as an option, it may be chosen in a context where the presence of a vascular system is assumed to be a given.

### Final Answer:
The correct answer is **All of the Above** (Option 4), as both the evolution of siponogamy and the development of secondary growth are crucial for the successful establishment of seed plants on land.