A garden in Devonshire, England, where Agatha Christie worked in a hospital pharmacy during World War I, before becoming the doyenne of mystery writers, is dedicated to growing all of the poisonous plants employed in her mysteries.

Dame Agatha wrote 80 whodunits, and somebody was poisoned in most of them. Her fictive criminals' favorite poison: cyanide. But they also used arsenic, strychnine, digitalis, morphine and taxine -- all derived from plants -- with deadly effect. Visitors to the garden are accosted by a large sign that warns "Do Not Touch." And each plant is labeled with one to five skulls, indicating its level of toxicity.

Here's a mystery closer to home: Somebody is poisoning the moose of Anchorage. It's probably you. And many of your relatives, friends, and neighbors. Because the entire city is a garden laced with poisonous plants.

I haven't noticed any skulls painted on signs in Anchorage, but some of the most poisonous plants in the Devonshire garden are in the Prunus family. Prunus species are popular ornamental trees in Anchorage, often going by the common names of chokecherry, bird cherry, and May Day tree.

Chokecherries are aptly named. Relatives of the cherry tree, they sport attractive blackish drupes, which have a high acid content, making them sour. The acidic fruits can choke or gag a person, but seldom cause death. Unless you are a moose or other ruminant.

This winter, at least three moose calves have died in Anchorage after browsing on chokecherry twigs. Dozens of moose are reported dead in Anchorage every winter, and it is possible that many more moose have succumbed to poisonous plants. It is difficult to inspect every moose found dead in the city, much less perform a detailed necropsy.

For all its imposing bulk and rugged good looks, a moose is a delicate creature. Its huge, four-chambered stomach, well adapted to digesting a winter diet of woody twigs, is particularly sensitive to physical and chemical agitations. Swallowing a few mouthfuls of chokecherry twigs, leaves or seeds can kill a moose in one to two hours. Calves are probably more vulnerable than adult moose because they are smaller.

The deadly ingredient in chokecherry foliage is cyanide gas: hydrogen cyanide or HCN. The cyanide is locked in plant cells, isolated from the enzymes that create the gas. However, wilting, freezing, crushing, and chewing (does this sound like what might happen to a plant eaten by a moose in winter?) releases the gas. So does digestion by the enzymes in a moose's rumen, the first of four chambers comprising its highly evolved stomach. A lethal dose of HCN causes rapid labored breathing, frothing at the mouth, dilated pupils, ataxia, muscle tremors, and convulsions. The moose usually dies within a few minutes of developing these symptoms. The cyanide stops cellular respiration, resulting in respiratory arrest. The moose suffocates.

The almond-like seed inside a peach pit is also capable of producing hydrogen cyanide. Egyptians and Romans used peach seeds to execute people. Hydrogen cyanide, aka Zyklon B, was employed in the Nazi gas chambers. This is seriously toxic stuff.

Fortunately, it's unlikely that you or I will be poisoned by HCN unless it is forced into our alimentary or respiratory systems by an agent of the Ptolemies, Caesars, or Nazis. Human stomachs are highly acidic, so HCN is released much more slowly than in the mildly acidic or alkaline contents of a rumen. And our stomachs don't have the high water content or microfloral enzymes of a moose rumen. Thank goodness, because in my curious youth I cracked a few peach pits and ate the seeds. They tasted and smelled like bitter almonds.

Hydrogen cyanide is also known as prussic acid, a compound preferred by many English murderers, if one is to believe the likes of Agatha Christie and other detective writers. A small dose inhaled by a bound captive or inadvertently self-administered in a nasal spray kills the victim in minutes, leaving no tell-tale clues. Except the smell of bitter almonds. Cagey killers leave a window open to disperse the smell.