Q.

Why don't penguins' feet get intolerably cold?

A.The penguins' feet do get cold, nearly freezing; in fact, the temperature of their toes has been measured at just about 32 degrees Fahrenheit. The birds have evolved a remarkable temperature control system in which blood warms the feet, but only enough to keep them functioning. The system is most efficient among the penguins of the Antarctic. The emperor penguin, for example, spends most of its life with its bare feet in direct contact with ice, snow or freezing water. If its feet were maintained at the same high temperature as the rest of its insulated body, precious heat would be lost quickly through conduction or convection. So the penguins evolved an anatomical arrangement in which arteries carrying warm blood toward the toes run side by side with veins carrying cold blood back in the opposite direction. The returning blood absorbs heat from the outflowing blood, and because of this efficient heat exchange, the circulation can be reduced to a level just high enough to keep the foot tissues alive. These foot tissues have special traits; they can survive with slowed circulation and conduct nerve impulses even when extremely cold. Also, penguins' feet, like those of ducks and other birds that spend time in cold water, are made up of lots of tendons and a minimum of musculature, and cold tendons are not as uncomfortable as cold muscles.

Q. Why don't plants repair themselves once they start turning brown, getting spots, etc.?

A.Plant cells are not like animal cells, and plant tissues do not heal themselves the way animal tissues do. But in the case of fungal or bacterial infections, the plant does try to contain the damage by producing phenolics, chemicals that are toxic to the invader. When the invader moves faster than the plant can react, the plant is overwhelmed by blight. Hazards that damage cell membranes, like freezing, often lead to the production of a gaseous hormone called ethylene. Ethylene induces senescence, that is, it starts the plant on a downhill course of aging. There are artificial chemicals that can control or reduce the effects of ethylene, but they are impractical to use on your begonia. Usually the youngest or growing parts of the plant are most resistant to stress, so the plant channels its energies into replacing, rather than repairing, its wounded leaves.

Readers are invited to submit questions about science to Questions, Science Times, The New York Times, 229 West 43d Street, New York, N.Y. 10036. Questions of general interest will be answered in this column, but requests for medical advice cannot be honored and unpublished letters cannot be answered individually.