lower and then secreted by the calyx, as in some species of Iris
and orchids. This latter being taken advantage of in Coronilla would
allow of the secretion within the flower ceasing, and as this change was
going on in the two secretions, all the parts of the flower would become
modified and correlated.

LETTER 716. TO J. BURDON SANDERSON. Down, Tuesday, September 9th [1873].

(716/1. Sir J. Burdon Sanderson showed that in Dionoea movement
is accompanied by electric disturbances closely analogous to those
occurring in muscle (see "Nature," 1874, pages 105, 127; "Proc. R. Soc."
XXI., and "Phil. Trans." Volume CLXXIII., 1883, where the results are
finally discussed).)

I will send up early to-morrow two plants [of Dionoea] with five goodish
leaves, which you will know by their being tied to sticks. Please
remember that the slightest touch, even by a hair, of the three
filaments on each lobe makes the leaf close, and it will not open for
twenty-four hours. You had better put 1/4 in. of water into the saucers
of the pots. The plants have been kept too cool in order to retard
them. You had better keep them rather warm (i.e. temperature of warm
greenhouse) for a day, and in a good light.

I am extremely glad you have undertaken this subject. If you get a
positive result, I should think you ought to publish it separately, and
I could quote it; or I should be most glad to introduce any note by you
into my account.

I have no idea whether it is troublesome to try with the thermo-electric
pile any change of temperature when the leaf closes. I could detect none
with a common thermometer. But if there is any change of temperature I
should expect it would occur some eight to twelve or twenty-four
hours after the leaf has been given a big smashed fly, and when it is
copiously secreting its acid digestive fluid.

I forgot to say that, as far as I can make out, the inferior surface of
the leaf is always in a state of tension, and that the contraction is
confined to the upper surface; so that when this contraction ceases or
suddenly fails (as by immersion in boiling water) the leaf opens again,
or more widely than is natural to it.

Whenever you have quite finished, I will send for the plants in their
basket. My son Frank is staying at 6, Queen Anne Street, and comes home
on Saturday afternoon, but you will not have finished by that time.

P.S. I have repeated my experiment on digestion in Drosera with complete
success. By gi