Final answer:
The development of a vascular system allowed for efficient transport of nutrients and water, contributing to the increase in size of plants.
Step-by-step explanation:
The development of a vascular system in plants contributed to an increase in their size mainly because it allowed for more efficient transport of nutrients and water. Vascular tissues, such as xylem and phloem, are responsible for conducting water, minerals, and food throughout the plant. By utilizing these specialized tissues, plants were able to grow larger and withstand periods of drought in harsh land environments. Additionally, the evolution of a root system enabled plants to absorb water and minerals from the soil, providing further support for larger plant growth.