David Walton - The Genius Plague

“How can a fungus know what trees most need nutrients?” Maisie asked, sounding skeptical.

“You’d be surprised. A fungus has all sorts of senses. It can determine the health of a tree, even detect animals moving around in the forest. Every time you step down”—Paul took an exaggerated step to demonstrate—“you’re stepping on a network of more than eight miles of microscopic mycelia, all intertwined beneath your foot. It can detect the pressure and the weight. When you lift your foot”—again, he demonstrated by lifting his own—“the mycelia immediately move out into the indentation, soaking up the moisture and detritus you left behind. You can’t see them, but they’re there.”

She shuddered. “Sounds creepy.”

Eventually, Paul found a nice patch of Favolus tenuiculus growing out of a stump. The white polypore mushrooms were lovely specimens of the type, their caps pocked with dozens of holes like a Swiss cheese. Maisie took one warily. “You’re sure they’re safe?”

“Quite sure,” he said, taking a bite. “This is what I do for a living. This variety is pretty common in the area. You could probably find it on restaurant menus back in Manaus.”

She smiled wanly. “I had been hoping you might take me out to dinner tonight.”

“There,” he said. “Wish granted.” They smiled at each other, but there was no joy in it.

The mushrooms tasted fine, but they stuck in Paul’s throat, and neither of them ate very much. Their main problem was not food, but water. River water, especially the swampy kind around them, was brackish and swarming with protozoa, bacteria, and viruses—not to mention millions of fungal spores—that could give them a wide array of illnesses. Paul had brought an ultraviolet light water purifier as well as chlorine dioxide tablets, but both were, of course, lost with his pack. They had no way to make a fire. Paul found some waxy leaves with rainwater pooled in them, which they dribbled into their mouths. It wasn’t much, but he hoped that they would make it back to civilization before it became a problem.

Night came quickly. It was murky under the trees even in the afternoon, but as the sun lowered, the shadows deepened, until they could barely see where they were going. “Let’s stop,” Paul said. “It’s dry here; it’s as good a place as any.”

The darkness, when it came, was complete. They had both been sleeping outside in the rainforest already, but this was different. Instead of mastering their environment, it felt like they were at its mercy. They leaned their backs together against a large tree, unwilling to put their heads down among the crawling things on the bare ground.

Paul sat awake, uncomfortable in his damp clothing. He had considered taking them off and hanging them to dry, but he knew from experience how bad the insects could be at night, and he wanted as much of his skin covered as possible, especially since they had no mosquito netting or bug spray. Beside him, Maisie shifted in the dark, as sleepless and uncomfortable as he.

“What’s that?” she asked.

He listened, thinking she had heard something, but a moment later realized that she was seeing something instead. As his eyes grew accustomed to the darkness, he saw a faint green glow resolve out of the gloom. He knew what it was. Foxfire.

“What’s foxfire?” she asked when he told her.

“Bioluminescent fungi. A lot of species excrete an oxidative enzyme that glows at night, attracting insects to help spread their spores. Kind of like bright flowers attracting pollinators. Watch this.” Paul clambered to his feet and felt his way carefully toward the glow. It was still extremely dark. He couldn’t actually see his feet, and he stumbled a few times before he found it. A dead log, about the size of his leg, emitting a faint green light along the cracked seams of its bark.

He picked it up. “Fungi are the great decomposers of the forest,” he said. “Any kind of dead organic material will be riddled through with mycelial strands within a few hours after death. Soil couldn’t exist without fungi breaking things down. They were the first organisms to colonize the land, a good hundred million years before plants.” He heaved the log into the woods. It struck a tree and exploded apart, sending a shower of green sparks through the air that illuminated them with an eerie green glow. Paul made his way back to her, able to see slightly now in the dim light.

“I can’t sleep,” she said. “I’m wet, and I’m scared, and I’m so angry I would kill those men right now, every one of them, without a second thought, if I had the chance. What were they doing? We never did anything to them. They just murdered a dozen people, for no reason at all. Why? Who would do something like that?”

Paul sat down next to her again. “There’s been a lot of nationalist sentiment in Pará and some of the other northern states,” he said. “People saying that Americans are ruining their country, wanting them to stay out, that sort of thing.”

“That’s stupid,” Maisie said. “Their whole economy is based on tourism.”

“Maybe a few of them took the sentiment too far.”

“No. That doesn’t make sense. These people were organized . If they weren’t Navy, then they stole a Navy boat and military uniforms. They had automatic weapons. This wasn’t a few guys with too much to drink taking their emotions out on a few Americans. They were too well outfitted for that.”

“You’re right. I don’t know who would want to do such a thing.”

“I just want to be home,” she said. “I want to be back in California, where things make sense.”

Paul couldn’t help it. He laughed, though he immediately regretted it. “I’m sorry,” he said. “I just never thought of California as making sense.”

She didn’t take offense. “More sense than they do here, anyway.”

The green glow hadn’t diminished. If anything, it had grown brighter, though maybe that was his eyes still adjusting. He could make out the expression on her face now, and see the basic lines of her body next to him. He stood, wanting to see what was left of the rotten log, but instead he saw something strange. Luminescent spots, more of them, stretching out into the distance. He squinted, trying to make sense of them in the darkness. It was hard to get a good idea of how far away they were, but they seemed to be forming two glowing lines. Straight, parallel lines. He shook his head, afraid he was hallucinating, but when he looked again, they were still there.

“Check this out,” he said.

Maisie joined him on her feet. The green splotches glowed brightly, and the lines were unmistakable. “It’s a path,” she said.

It certainly looked like one. But what kind of path would be illuminated by fungi? Paul stepped forward, then bent down and examined the first of the spots, which was on the side of a tree. The tree itself was covered in fungal patches, and a few conks grew from one side, but only this single patch was glowing. He walked to the next patch, this one on the ground, and found the same thing—an area full of fungi, but only this one small patch glowing. What was going on?

“We should follow it,” Maisie said.

“What?”

“It’s got to be man-made, right? Nothing organic goes in straight lines like that. If it’s a human path, then it has to lead somewhere.”

Paul couldn’t argue with her reasoning, but neither did he know of any way a human could make a path out of selectively triggered bioluminescent fungi. “It is leading in the direction we want to go,” he said, shrugging.

“And it’s not like we’re getting any sleep. I don’t want to sit here all night feeling sorry for myself and getting sick. I want to get home.”