A: A tree's vital organs don't stop growing, as animals' eventually do. Rather, if they manage to withstand the stresses you mention, they'll ultimately grow themselves to death. Trees are genetically programmed to continuously increase in mass, endlessly producing new leaves, new layers of wood, and new branches. They can even prevent the spread of infection from limb to limb. But these engines of longevity are the tree's ultimate undoing. No organism can maintain itself without a sufficient energy supply, and the energy a healthy tree requires increases significantly as it grows taller; a tree that doubles in height, for example, might require four times as much energy as it did before its growth spurt. To keep its appetite under control, a tree allows up to 90 percent of its bark and xylem (the woody tissue below the bark) to die off so that it has to maintain only 10 percent of its mass. Eventually, though, even this internal triage doesn't keep the plant alive. It grows so large that it can no longer absorb enough nutrients and manufacture enough energy through photosynthesis to sustain itself. Sometime before its 7,000thbirthday—the age of the world's oldest living tree, a 238-foot-tall redwood in Prairie Creek Redwood State Park, California—its weakened physiology fails or succumbs to disease."Theoretically these systems could last forever," says arborist Alex Shigo, author of the leading textbook A New Tree Biology, "but every system has its limits."

Q:Is it true that the Inuit have 20 different words for snow?
—C. Knutsen, New York, New York

A:At least 20, depending on your dictionary. According to The Kobuk Iñupiaq Dictionary, used in schools throughout northwestern Alaska, there are 23 words in the Inuit language, Iñupiaq, to describe winter's powdery precip. Only three—qannik, aniu, and apun—specifically translate as "snow on the ground." The other 20 detail myriad other snowy incarnations, among them auksalak ("melting snow") and pukak ("sugar snow thawed to make drinking water"). How can so few syllables say so much? Unlike English, Iñupiaq is a polysynthetic language—dozens of affixes can add nuance to the meaning of a simple noun like snow. According to West Greenlandic, an Inuit dictionary that has a whopping 49 words for both snow and ice, qanipalaat means "feathery clumps of falling snow," and then there's qiqsruqqaq ("glaze on snow in thaw time"), and the deadly sisuuk ("wet snow that can slide and cause an avalanche"). "Our lives," explains Lorena Williams Kapniaq, an Iñupiaq instructor at the University of Alaska, Fairbanks, "are centered around snow."

Rick Sealock

A:A pooch who pokes its nose into the business end of another is sussing out a number of social cues. Dogs secrete pheromones, subtly smelly hydrocarbons, from many glands located in and around their genitals; these odors let others know if they're sniffing an old friend (dogs can recognize each other by smell after years of separation), and whether there's the possibility of mating (females in heat excrete pheromones so strong they can be detected blocks away). Most important, canines locate themselves in the dog hierarchy with a few sniffs. When approached by a dominant dog, a submissive pup will secrete from its anal glands the pungent scent of fear. We'll pass on trying to describe it and the potpourri of other canine olfactory signals, because—thankfully—for the most part, our noses aren't sensitive enough to detect them. "Dogs smell in technicolor, and we smell in black and white," says Stephen Zawistowski, an animal behaviorist with the American Society for the Prevention of Cruelty to Animals. "Trying to explain what a dog smells is like trying to describe a rainbow to a blind person."

Q:Why do parts of my body sometimes feel cold to the touch when I don't actually feel cold in those places?
—Julie Colhoun, San Francisco, California

A:The feeling of being cold—a sensation brought on when your core temperature is threatened but at 98.6 degrees is still quite warm—and finding your skin cold to the touch are two very different things, caused by two separate physiological processes. In fact, cold skin (usually found in fatty areas like the stomach, thighs, cheeks, and buttocks) helps you feel warmer on the inside. Here's how: The body protects its vital organs from the cold by retaining as much heat as possible within its core. In environments below 65 degrees Fahrenheit, your circulatory system limits the amount of 98.6-degree blood flowing to your outer layers through a process called vasoconstriction: Smooth muscles in the tiny arteries of the skin contract, and this narrowing decreases blood flow, curtailing heat loss, while making your outermost layer feel cold to the touch. But because vasoconstriction only slows the loss of heat from your core, it can't keep you toasty on its own if you stay out too long or if the temperature drops even five degrees more. If cool turns to cold, your core temperature becomes threatened and your insides start to feel like your outsides—chilly. Your adrenal glands kick in, your metabolism quickens, and the extraenergy burned warms your core.   

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