Readers discuss ancient plagues and a fern’s leaf revival

Under the weather

New climate reconstructions show that periods of decreasing temperature and rainfall coincided with three plagues that struck the Roman Empire, Bruce Bower reported in “Did climate drive ancient plagues?” (SN: 2/24/24, p. 13).

Bower reported that researchers are uncertain exactly how those climate shifts may have influenced the plagues’ spread. Reader Robert J. MacCoun asked if one explanation could be that the colder conditions drove people to spend more time indoors with poor ventilation.

Cold periods do “tend to bring people indoors, closer together, increasing the chances of spreading infectious disease,” says classical archaeologist Brandon McDonald of the University of Basel in Switzerland. But this is just one of many ways that climate shifts can impact disease spread. Identifying the pathogen behind an infectious disease is a crucial part of the puzzle, McDonald says. That’s because some changes in temperature and precipitation are advantageous to certain pathogens and the animals that spread them but disadvantageous to others.

“For most Roman period [disease] events, we haven’t yet scientifically determined the pathogenic cause,” McDonald says. While the new findings are noteworthy, he says, researchers need to know more about the diseases and their ecology to determine how climate may have influenced their spread.

Pioneering plants

A Panamanian tree fern is the first known plant that turns dead leaves into roots that seek out nutrient-rich soil, Darren Incorvaia reported in “Fern revives dead leaves” (SN: 2/24/24, p. 5).

Reader Douglas B. Quine was surprised that the discovery was considered novel, given that the leaf-into-roots process seems similar to the widespread practice of propagating plants using leaf cuttings.

The root formation observed in the fern, called Cyathea rojasiana, is a different process from propagation through leaf cuttings, says tropical forest ecologist James Dalling of the University of Illinois Urbana-Champaign. In cuttings, new roots and leaves are created in the leaf or leafstalk and differentiate into completely new leaf and root tissue. “The original leaf dies,” Dalling says. “In C. rojasiana, the original leaf loses its photosynthetic function and partially decomposes but continues to live for many years, functioning as a root. In this case, the vascular tissue of the leaf is repurposed.”