CD's observations on preference of Drosera for milk and nitrogenous fluids, and the effect of nitrate of ammonia are interesting. Asks whether CD is satisfied that the effect is not due to density of fluid or to a chemical irritant. His own observations suggest such possibilities.
My dear Sir,
Your observations upon the sensible little Drosera, preferring milk &
nitrogenous fluids,—also the effect of Nit. Am
But I am by no means sure whether I can shew that it is a question of density (or Endosmose &c, rather), for I've thought it possible the gum sol. might, by virtue of its adhesiveness (?) &c. in some way or other deceive me.
On Tuesday P.M. (2--2.15) a drop of milk, of syrup, & of gum placed on 3 several leaves of the Drosera. In each case several of the marginal hairs of the rounded extreme of the leaf were patent or erect.
4.45. Gum drop most conspicuously, by far, affected.
But 2 glands are left sticking right out. Nearly all the rest are more
or less incurved—right into—the drop.— In the milk
& syrup not much change noted, perhaps the latter more
4.50 a drop of gum placed on another leaf. All the marginal glands perfect. The leaf supported by a slip of glass.— at 6.8 no incurving notable
Wednesday. 8.36. All the glands of the last (4.50) leaf remarkably
incurved.— In the old gum-drop no marked further
change,—but 1 gland now sticks
Milk, no very marked change,—prob
I dont know how far you have tried various fluids or whether further experiments are needed to settle the Nitrogenous part of the Curving.
The progress of change is not easy to describe without minute observation or perhaps drawings.— A series of wee photographs might do the work nicely.—
Very faithfully yours | Dan
Chas. Darwin, esq.
- f1 2921.f1See letters to Daniel Oliver, 11 September  and 15 [September 1860].
- f2 2921.f2This was opposed to CD's view that only nitrogenous matter caused the inflection of the leaves.
- f3 2921.f3The term `endosmose' was coined by Ren´e Joachim Henri Dutrochet. He established that `when two liquids of different densities or of different chemical natures are separated by a membranous partition, two currents are established across this partition, going in opposite directions, and unequal in force'. Dutrochet called the movement of fluid into organic tissue under these conditions `endosmose'. See Dutrochet 1828, p. 1.