aggregation could be seen travelling rapidly down the cells of the
tentacles; and the granules of protoplasm soon united into spheres and
variously shaped masses, which displayed the usual move- [page 281]
ments. Half a minim of a solution of one part of nitrate of ammonia to
146 of water was next placed on the centre of a leaf; after 6 hrs. some
marginal tentacles on both sides were inflected, and after 9 hrs. they
met in the centre. The lateral edges of the leaf also became incurved,
so that it formed a half-cylinder; but the apex of the leaf in none of
my few trials was inflected. The above dose of the nitrate (viz. 1/320
of a grain, or .202 mg.) was too powerful, for in the course of 23 hrs.
the leaf died.
Drosera filiformis. This North American species grows in such abundance
in parts of New Jersey as almost to cover the ground. It catches,
according to Mrs. Treat,* an extraordinary number of small and large
insects, even great flies of the genus Asilus, moths, and butterflies.
The specimen which I examined, sent me by Dr. Hooker, had thread-like
leaves, from 6 to 12 inches in length, with the upper surface convex
and the lower flat and slightly channelled. The whole convex surface,
down to the roots for there is no distinct footstalk is covered with
short gland-bearing tentacles, those on the margins being the longest
and reflexed. Bits of meat placed on the glands of some tentacles
caused them to be slightly inflected in 20 m.; but the plant was not in
a vigorous state. After 6 hrs. they moved through an angle of 90o, and
in 24 hrs. reached the centre. The surrounding tentacles by this time
began to curve inwards. Ultimately a large drop of extremely viscid,
slightly acid secretion was poured over the meat from the united
glands. Several other glands were touched with a little saliva, and the
tentacles became incurved in under 1 hr., and re-expanded after 18 hrs.
Particles of glass, cork, cinders, thread, and gold-leaf, were placed
on numerous glands on two leaves; in about 1 hr. four tentacles became
curved, and four others after an additional interval of 2 hrs. 30 m. I
never once succeeded in causing any movement by repeatedly touching the
glands with a needle; and Mrs. Treat made similar trials for me with no
success. Small flies were placed on several leaves near their tips, but
the thread-like blade became only on one occasion very slightly bent,
directly beneath the insect. Perhaps this indicates that the blades of
vigorous plants would bend over captured insects, and Dr. Canby informs
me that this is the case; but the movement cannot be strongly
pronounced, as it was not observed by Mrs. Treat.
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