The nature of the liquor perspired has been already noticed, p. 68. In hot weather it has been observed by Hales, Du Hamel and Guettard to partake occasionally of the peculiar scent of the plant that yields it, but in general the odorous matter is of too oily a nature to be combined with it.
The sensible perspiration of plants is of various kinds. When watery, it can be considered only as a condensation of their insensible evaporation, perhaps from some sudden change in the atmosphere. Groves of Poplar or Willow exhibit this phenomenon, even in England, in hot calm weather, when drops of clear water trickle from their leaves like a slight shower of rain. Sometimes it is of a saccharine nature, as De la Hire observed in Orange trees; Du Hamel Arb. v. 1. 150. It is more glutinous in the Tilia or Lime-tree, more resinous in Poplars, as well as in Cistus creticus, from which last the resin called Labdanum is collected, by beating the shrub with leather thongs. See Tournefort's Voyage, 29. In the Fraxinella, Dictamnus albus, it is a highly inflammable vapour. Ovid has made an elegant use of the
