Many plants store sugar in the form of starch in underground structures (think potatoes or beets). In the spring new leaves must be formed before the plant can begin photosynthesizing again. Which statement below offers a plausible explanation of the function of phloem in plants like potatoes and beets?
A. The roots are source cells in the summer and winter but not in the spring and fall.
B. The leaves are source cells during the summer and the roots are the source cells in the early spring.
C. The flow of sugars is in the direction of sink to source.
D. When the leaves are forming in the spring, phloem flow stops