Note 11 — Chapter VI · MODIFIED CIRCUMNUTATION: SLEEP OR NYCTITROPIC MOVEMENTS, THEIR USE: SLEEP OF COTYLEDONS.
Reading edition
Cassia laevigata was exposed to a clear sky for 35 m., and C. calliantha (a Guiana species) for 60 m., the temperature on the surrounding grass being –2° C., and neither was in the least injured. But when C. laevigata was exposed for 1 h., the temp. on the surrounding grass being between –3° and –4° C., every leaf was killed.