[17] Our common larch, like almost every other kind of tree, consists of numberless varieties, which differ considerably in quickness of growth, ultimate size, and value of timber. This subject has been much neglected. We are, however, on the eve of great improvements in arboriculture; the qualities and habits of varieties are just beginning to be studied. It is also found that the uniformity in each kind of wild growing plants called _species_, may be broken down by art or culture, and that when once a breach is made, there is almost no limit to disorder; the _mele_ that ensues being nearly incapable of reduction. [18] There is yet no sufficient data for the term alpine plant, but with reference to latitude. The influence on vegetables, arising from rarefaction and diminution of pressure of atmosphere, from difference of stimulus of solar ray—when the entire ray of light, heat, and chemical power, though less intense, is radiated fresh, and not much broken or modified by refraction and reflection, and heat communicated more in proportion by radiation than by contact of heated air; or from difference of electric or galvanic or other meteoric impression connected with altitude or ranges of mountains, or with primary rocks or more upright strata, has not been made the subject of research, at least has not been sufficiently investigated by any naturalist. [19] 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. [20] We have had no experience of larch, excepting very young, growing on chalk and its affinities. We are told there are a few instances where larch has reached 50 years in these calcareous soils, some distance south of London. This merits attention. [21] “Oh! the bonny blooming heather.”—“Man has spoken evil things of the sun, of love, and of life.”