occasion in nearly so short a time as an hour. These cases of the
simultaneous darkening or blackening of the glands from the action of
weak solutions are important, as they show that all the glands absorbed
the carbonate within the same time, which fact indeed there was not the
least reason to doubt. So again, whenever all the [page 145] tentacles
become inflected within the same time, we have evidence, as before
remarked, of simultaneous absorption. I did not count the number of
glands on these four leaves; but as they were fine ones, and as we know
that the average number of glands on thirty-one leaves was 192, we may
safely assume that each bore on an average at least 170; and if so,
each blackened gland could have absorbed only 1/54400 of a grain
(.00119 mg.) of the carbonate.
A large number of trials had been previously made with solutions of one
part of the nitrate and phosphate of ammonia to 43750 of water (i.e.
one grain to 100 ounces), and these were found highly efficient.
Fourteen leaves were therefore placed, each in thirty minims of a
solution of one part of the carbonate to the above quantity of water;
so that each leaf received 1/1600 of a grain (.0405 mg.). The glands
were not much darkened. Ten of the leaves were not affected, or only
very slightly so. Four, however, were strongly affected; the first
having all the tentacles, except forty, inflected in 47 m.; in 6 hrs.
30 m. all except eight; and after 4 hrs. the blade itself. The second
leaf after 9 m. had all its tentacles except nine inflected; after 6
hrs. 30 m. these nine were sub-inflected; the blade having become much
inflected in 4 hrs. The third leaf after 1 hr. 6 m. had all but forty
tentacles inflected. The fourth, after 2 hrs. 5 m., had about half its
tentacles and after 4 hrs. all but forty-five inflected. Leaves which
were immersed in water at the same time were not at all affected, with
the exception of one; and this not until 8 hrs. had elapsed. Hence
there can be no doubt that a highly sensitive leaf, if immersed in a
solution, so that all the glands are enabled to absorb, is acted on by
1/1600 of a grain of the carbonate. Assuming that the leaf, which was a
large one, and which had all its tentacles excepting eight inflected,
bore 170 glands, each gland could have absorbed only 1/268800 of a
grain (.00024 mg.); yet this sufficed to act on each of the 162
tentacles which were inflected. But as only four out of the above
fourteen leaves were plainly affected, this is nearly the minimum dose
which is efficient.
126