He had just finished reading Doctor Zhivago, a book that incited him to scribble excited notes in the margins and underline several passages:

Lara walked along the tracks following a path worn by pilgrims and then turned into the fields. Here she stopped and, closing her eyes, took a deep breath of the flower-scented air of the broad expanse around her. It was dearer to her than her kin, better than a lover, wiser than a book. For a moment she rediscovered the purpose of her life. She was here on earth to grasp the meaning of its wild enchantment and to call each thing by its right name, or, if this were not within her power, to give birth out of love for life to successors who would do it in her place.

“NATURE/PURITY,” he printed in bold characters at the top of the page.

Oh, how one wishes sometimes to escape from the meaningless dullness of human eloquence, from all those sublime phrases, to take refuge in nature, apparently so inarticulate, or in the wordlessness of long, grinding labor, of sound sleep, of true music, or of a human understanding rendered speechless by emotion!

McCandless starred and bracketed the paragraph and circled “refuge in nature” in black ink.

Next to “And so it turned out that only a life similar to the life of those around us, merging with it without a ripple, is genuine life, and that an unshared happiness is not happiness… And this was most vexing of all,” he noted, “HAPPINESS ONLY REAL WHEN SHARED.”

It is tempting to regard this latter notation as further evidence that McCandless’s long, lonely sabbatical had changed him in some significant way. It can be interpreted to mean that he was ready, perhaps, to shed a little of the armor he wore around his heart, that upon returning to civilization, he intended to abandon the life of a solitary vagabond, stop running so hard from intimacy, and become a member of the human community. But we will never know, because Doctor Zhivago was the last book Chris McCandless would ever read.

Two days after he finished the book, on July 30, there is an ominous entry in the journal: “EXTREMLY WEAK. FAULT OF POT. SEED. MUCH TROUBLE JUST TO STAND UP. STARVING. GREAT JEOPARDY.” Before this note there is nothing in the journal to suggest that McCandless was in dire circumstances. He was hungry, and his meager diet had pared his body down to a feral scrawn of gristle and bone, but he seemed to be in reasonably good health. Then, after July 30, his physical condition suddenly went to hell. By August 19, he was dead.

There has been a great deal of conjecture about what caused such a precipitous decline. In the days following the identification of McCandless’s remains, Wayne Westerberg vaguely recalled that Chris might have purchased some seeds in South Dakota before heading north, including perhaps some potato seeds, with which he intended to plant a vegetable garden after getting established in the bush. According to one theory, McCand-less never got around to planting the garden (I saw no evidence of a garden in the vicinity of the bus) and by late July had grown hungry enough to eat the seeds, which poisoned him.

Potato seeds are in fact mildly toxic after they’ve begun to sprout. They contain solanine, a poison that occurs in plants of the nightshade family, which causes vomiting, diarrhea, headache, and lethargy in the short term, and adversely affects heart rate and blood pressure when ingested over an extended period. This theory has a serious flaw, however: In order for McCandless to have been incapacitated by potato seeds, he would have had to eat many, many pounds of them; and given the light weight of his pack when Gallien dropped him off, it is extremely unlikely that he carried more than a few grams of potato seeds, if he carried any at all.

But other scenarios involve potato seeds of an entirely different variety, and these scenarios are more plausible. Pages 126 and 127 of Tanaina Plantlore describe a plant that is called wild potato by the Dena’ina Indians, who harvested its carrotlike root. The plant, known to botanists as Hedysarum alpinum, grows in gravelly soil throughout the region.

According to Tanaina Plantlore, “The root of the wild potato is probably the most important food of the Dena’ina, other than wild fruit. They eat it in a variety of ways-raw, boiled, baked, or fried-and enjoy it especially dipped in oil or lard, in which they also preserve it.” The citation goes on to say that the best time to dig wild potatoes “is in the spring as soon as the ground thaws… During the summer they evidently become dry and tough.”

Priscilla Russell Kari, the author of Tanaina Plantlore, explained to me that “spring was a really hard time for the Dena’ina people, particularly in the past. Often the game they depended on for food didn’t show up, or the fish didn’t start running on time. So they depended on wild potatoes as a major staple until the fish came in late spring. It has a very sweet taste. It was-and still is- something they really like to eat.”

Above ground the wild potato grows as a bushy herb, two feet tall, with stalks of delicate pink flowers reminiscent of miniature sweet-pea blossoms. Taking a cue from Kari’s book, McCandless started to dig and eat wild potato roots on June 24, apparently without ill effect. On July 14, he began consuming the pealike seed pods of the plant as well, probably because the roots were becoming too tough to eat. A photograph he took during this period shows a one-gallon Ziploc plastic bag stuffed to overflowing with such seeds. And then, on July 30, the entry in his journal reads, “EXTREMLY WEAK. FAULT OF POT. SEED…”

One page after Tanaina Plantlore enumerates the wild potato, it describes a closely related species, wild sweet pea, Hedysarum mackenzii. Although a slightly smaller plant, wild sweet pea looks so much like wild potato that even expert botanists sometimes have trouble telling the species apart. There is only a single distinguishing characteristic that is absolutely reliable: On the underside of the wild potato’s tiny green leaflets are conspicuous lateral veins; such veins are invisible on the leaflets of the wild sweet pea.

Kari’s book warns that because wild sweet pea is so difficult to distinguish from wild potato and “is reported to be poisonous, care should be taken to identify them accurately before attempting to use the wild potato as food.” Accounts of individuals being poisoned from eating H. mackenzii are nonexistent in modern medical literature, but the aboriginal inhabitants of the North have apparently known for millennia that wild sweet pea is toxic and remain extremely careful not to confuse H. alpinum with H. mackenzii.

To find a documented poisoning attributable to wild sweet pea, I had to go all the way back to the nineteenth-century annals of Arctic exploration. I came across what I was looking for in the journals of Sir John Richardson, a famous Scottish surgeon, naturalist, and explorer. He’d been a member of the hapless Sir John Franklin s first two expeditions and had survived both of them; it was Richardson who executed, by gunshot, the suspected murderer-cannibal on the first expedition. Richardson also happened to be the botanist who first wrote a scientific description of H. mackenzii and gave the plant its botanical name. In 1848, while leading an expedition through the Canadian Arctic in search of the by then missing Franklin, Richardson made a botanical comparison of H. alpinum and H. mackenzii. H. alpinum, he observed in his journal,

furnishes long flexible roots, which taste sweet like the liquorice, and are much eaten in the spring by the natives, but become woody and lose their juiciness and crispness as the season advances. The root of the hoary, decumbent, and less elegant, but larger-flowered Hedysarum mackenzii is poisonous, and nearly killed an old Indian woman at Fort Simpson, who had mistaken it for that of the preceding species. Fortunately, it proved emetic; and her stomach having rejected all that she had swallowed, she was restored to health, though her recovery was for some time doubtful.