sentences:  Some plants produce stems modified to store energy and preserve a location of potential growth to survive a cold or dry period which normally is a period of inactive growth, and when that period is over the plants resume new growth from the underground stems.Being underground protects the stems from the elements during the dormancy period, such as freezing and thawing in winter or extreme heat and drought in summer or fire.They can also protect plants from heavy grazing pressure from animals, the plant might be eaten to the ground but new growth can occur from below ground stem that can not be reached by the herbivores.