Final answer:
The vascular system, including both xylem and phloem tissues, is the plant adaptation responsible for the development of primary growth, enabling true leaves and roots' evolution that facilitate extended growth and resource uptake.
Step-by-step explanation:
The plant adaptation responsible for the development of primary growth is the vascular system. This system comprises xylem tissue, which transports water and minerals, and phloem tissue, which moves sugars and proteins. The emergence of vascular tissue enabled the development of true leaves for photosynthesis and roots for water uptake from the soil. Primary growth allows plants to extend their shoots and roots, thereby enabling them to grow taller and to access more resources, which is vital for survival on land.
Apical meristem tissue is another crucial adaptation related to primary growth. This tissue is present at the tips of roots and shoots, contributing to the growth in length of plants. It represents the active, undifferentiated cells that divide and allow plants to increase in height and expand their root systems.