combining correct observations with a faulty inference.


"4. As the upper surface of leaves constitutes the organ of
respiration, on which the sap is exposed in the termination of
arteries beneath a thin pellicle to the action of the atmosphere,
these surfaces in many plants strongly repel moisture, as cabbage
leaves, whence the particles of rain lying over their surfaces
without touching them, as observed by Mr. Melville (Essays
Literary and Philosophical: Edinburgh), have the appearance of
globules of quicksilver. And hence leaves with the upper
surfaces on water wither as soon as in the dry air, but continue
green for many days if placed with the under surface on water, as
appears in the experiments of Monsieur Bonnet (Usage des
Feuilles). Hence some aquatic plants, as the water-lily
(Nymphoea), have the lower sides floating on the water, while the
upper surfaces remain dry in the air.

"5. As those insects which have many spiracula, or breathing
apertures, as wasps and flies, are immediately suffocated by
pouring oil upon them, I carefully covered with oil the surfaces
of several leaves of phlomis, of Portugal laurel, and balsams,
and though it would not regularly adhere, I found them all die in
a day or two.

"It must be added that many leaves are furnished with muscles
about their foot-stalks, to turn their surfaces to the air or
light, as mimosa or Hedysarum gyrans. From all these analogies I
think there can be no doubt but that leaves of trees are their
lungs, giving out a phlogistic material to the atmosphere, and