128. Amīr al-mu’minīn, peace be upon him, said: Guard against cold in its (seasonal) beginning and welcome it towards its end because it effects bodies in the same way as it effects plants. In the beginning, it destroys them but in the end it gives them fresh leaves. 
 During autumn, protection from cold is necessary because with the change of weather the temperature of the body also changes and ailments such as flue, catarrh, cough etc., occur. This is because bodies are accustomed to hot weather and when suddenly cold comes on tissues become contracted and cold dryness increases in the body. Thus, bathing with cold water soon after bathing with hot water is harmful for this very reason that with hot water the tissues expand and so they at once admit the effect of cold water, and in consequence the natural heat of the body is affected. On the other hand, there is no need of protection from cold during spring season nor is it harmful for the health, because the body is already accustomed to cold. Thus, the temperate cold of the spring is not unpleasant to the body. Rather, with the decline of cold there is an increase of heat and dampness in the body as a result of which growth gets impetus, natural heat rises, the body grows, the temperament feels pleasant and the spirit is joyful.
Similarly, there is the same effect in the plant world. Thus, during autumn due to the prevalence of coldness and dryness, the leaves wither, the vegetative power decreases, the freshness of the plants fades and there is a death-like effect on the green areas. Spring brings the message of life for them. Then with the blowing of healthy winds the blossoms begin to sprout, plants become fresh and healthy, and forests and wildernesses acquire a green hue.