Note 19 — PART II. BRITISH FOREST TREES USED AS NAVAL TIMBER.

When water is stationary, either in the pores of the soil or by itself, if the temperature be not very low, a slight putrefaction generally commences, aided by the dead vegetable or animal matter contained in the soil or the water; and it is only the more robust aquatic vegetables whose juices are not corrupted, from their roots being soaked in this tainted fluid. It would appear, too, that the aqueous part of the atmosphere is also susceptible of the same putrid changes, although in general the putrescency may have commenced before the evaporation. This condition of the aqueous part of the atmosphere is a disposing cause to blight or mildew in vegetables, and remittent, intermittent, and putrid fevers in man. Mill-ponds are notorious both for mildew and agues.