Four leaves had been pinned out
horizontally, and 2 of these suffered more than those above or below on the
same branches, which had been allowed to go to sleep. It is rather a
remarkable fact that some plants of Lotus Jacoboeus, an inhabitant of so
hot a country as the Cape Verde Islands, were exposed one night to a clear
sky, with the temperature of the surrounding grass -2o C., and on a second
night for 30 m. with the temperature of the grass between -3o and -4o C.,
and not a single leaf, either the pinned-out or free ones, was in the least
injured.
Marsilea quadrifoliata.--A large plant of this species--the only
Cryptogamic plant known to sleep--with some leaves pinned open, was exposed
for 1 h. 35 m. to a clear sky, the temperature on the surrounding ground
being -2o C., and not a single leaf was injured. After an interval of some
days the plant was again exposed for 1 h. to a clear sky, with the
temperature on the surrounding ground lower, viz., -4o C. Six leaves had
been pinned out horizontally, and all of them were utterly killed. The
plant had emitted long trailing stems, and these had been wrapped round
with a blanket, so as to protect them from the frozen ground and from
radiation; but a very large number of leaves were left freely exposed,
which had gone to sleep, and of these only 12 were killed.
Pages:
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489