Medicinal Plants

To solve the problem, we need to identify which part of the plant an aphid targets to extract plant juices.

1. Role of Phloem Sieve Tubes:
The phloem is a vascular tissue in plants responsible for the transport of nutrients, especially sugars (produced via photosynthesis), throughout the plant.
Sieve tubes are a component of the phloem that help in this translocation of food.
Aphids are small sap-sucking insects that feed on these sugary solutions by piercing their proboscis into the phloem sieve tubes.

2. Elimination of Other Options:
- Xylem: Transports water and minerals, not sugars.
- Cambium: Meristematic tissue, not involved in sap transport.
- Pith: Storage tissue in the center, not the main source of plant sap.

Final Answer:
An aphid pierces its proboscis into the to get plant juices.