When grafting a plant, which of the following layers of both plant and graft must come into contact? a. wood
b. pith
c. cambium
d. xylem

Explanation:

For successful grafting to take place, the vascular cambium tissues of the stock and scion plants must be placed in contact with each other. Both tissues must be kept alive until the graft has "taken", usually a period of a few weeks.

the answer is: they occur when the sun, moon, and earth are aligned. in spite of their name, these tides occur twice a year in the spring and fall.