Cress seeds (Lepidum sativum) of the previous year were placed on four
leaves; two of these next morning were moderately and two strongly
inflected, and remained so for four, five, and even six days. Soon
after these seeds were placed on the leaves and had become damp, they
secreted in the usual manner a layer of tenacious mucus; and to
ascertain whether it was the absorption of this substance by the glands
which caused so much inflection, two seeds were put into water, and as
much of the mucus as possible scraped off. They were then placed on
leaves, which became very strongly inflected in the course of 3 hrs.,
and were still closely inflected on the third day; so that it evidently
was not the mucus which excited so [page 128] much inflection; on the
contrary, this served to a certain extent as a protection to the seeds.
Two of the six seeds germinated whilst still lying on the leaves, but
the seedlings, when transferred to damp sand, soon died; of the other
four seeds, only one germinated.
Two seeds of mustard (Sinapis nigra), two of celery (Apium
graveolens) both of the previous year, two seeds well soaked of caraway
(Carum carui), and two of wheat, did not excite the leaves more than
inorganic objects often do. Five seeds, hardly ripe, of a buttercup
(Ranunculus), and two fresh seeds of Anemone nemorosa, induced only a
little more effect. On the other hand, four seeds, perhaps not quite
ripe, of Carex sylvatica caused the leaves on which they were placed to
be very strongly inflected; and these only began to re-expand on the
third day, one remaining inflected for seven days.
It follows from these few facts that different kinds of seeds excite
the leaves in very different degrees; whether this is solely due to the
nature of their coats is not clear. In the case of the cress seeds, the
partial removal of the layer of mucus hastened the inflection of the
tentacles. Whenever the leaves remain inflected during several days
over seeds, it is clear that they absorb some matter from them. That
the secretion penetrates their coats is also evident from the large
proportion of cabbage, raddish, and cress seeds which were killed, and
from several of the seedlings being greatly injured. This injury to the
seeds and seedlings may, however, be due solely to the acid of the
secretion, and not to any process of digestion; for Mr. Traherne
Moggridge has shown that very weak acids of the acetic series are
highly injurious to seeds. It never occurred to me to observe whether
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