How smoke makes a wildflower grow.

After 15 years and some 50,000 seeds that refused to come up, researchers have finally cracked the mystery of how to sprout one of California's more puzzling wildflowers.

In nature, the bleeding heart Dicentra chrysantha springs up freely after fire scorches dry, scrubby chaparral landscape. Yet Jon E. Keeley of the U.S. Geological Survey in Three Rivers, Calif., and C.J. Fotheringham of California State University, Los Angeles spent years failing to find the right triggers to germinate seeds in the laboratory.

The secret is burying the seeds in soil for a year and then exposing them to a 10-minute puff of smoke, the researchers report in the October Ecology. The paper describes 25 chaparral species that respond not to a fire's heat but to its smoke. Only a few of the species need burial before sprouting.

Last year, Keeley and his colleagues announced finding the first North American wildflower to need smoke to get growing (SN: 5/31/97, p. 334). Keeley suspects that not all the smoke-sensitive chaparral plants respond via the same biochemical pathways. For example, the 10-minute exposure needed by bleeding hearts kills seeds of the first smoker plant he found, the whispering bell, which needs just a minute of smoke.