Read the following passage.
A. Mycorrhizae are partnerships between plant roots and fungi, and the name itself means fungus root. Scientists think about 95 per cent of all seed plants have them on their roots, and both partners probably need them to survive in the wild. The plant gains a better ability to absorb minerals such as phosphorus and nitrogen, and it resists root diseases more strongly. In return, the fungus takes sugars directly from the plant, so it does not have to compete with other microorganisms for its food.
B. These partnerships take several forms. The most widespread form, called arbuscular mycorrhizae, is found in about 90 per cent of seed plants, and in it the fungus grows inside the cells of the root's outer layer. In the other main form, ectomycorrhizae, the fungus wraps the root in a thick sheath that often makes it several times wider, and its threads pass between root cells without entering them. This form is especially well developed in Canada, where most forests are dominated by trees that carry it.
C. The fungi grow many branching threads, called mycelium, that spread out from a root tip and can join the roots of other trees and plants. Plants linked in this way share what scientists call a common mycorrhizal network. In 1997, a team including Suzanne Simard, now a forest ecologist at the University of British Columbia, reported in the journal Nature that carbon moved in both directions between birch and Douglas fir seedlings in the field. The Douglas fir gained more than it gave, and its net gain averaged 6 per cent of the carbon it took up through photosynthesis. Such a forest network is now widely known as the wood-wide web.
D. Simard now leads the Mother Tree Project, a 100-year study of different harvesting approaches in the Douglas fir forests of British Columbia's Interior. How much the networks matter is still debated, however. In 2023, Justine Karst of the University of Alberta and two colleagues reviewed the field evidence. They judged that claims that the networks are widespread and that they pass useful resources to seedlings are not well supported. They also found no peer-reviewed evidence that mature trees send extra resources to their own offspring, and concluded that knowledge of the networks is too sparse and unsettled to guide forest management.
E. Not given in any of the above paragraphs.
Decide which paragraph, A to D, has the information given in each statement below. Select E if the information is not given in any of the paragraphs.