Complex sentence: They can be in a resting state overwinter or when conditions are dry, then start growth when conditions are suitable, the buds before they start growing into stem, leaves, or flowers are said to be in an embryonic state.
Split into simpler sentences: They can be in a resting state over winter or when conditions are dry, and then commence growth when conditions become suitable. Before they start growing into stem, leaves, or flowers, the buds are said to be in an embryonic state.