746 SUB ANT ARCTIC ISLANDS OF NEW ZEALAND. [Soils and Soil- formers. 



posed plant-remains which are variously designated "humus," "peat," "black 

 earth," "mould," or, in America, "tule," or by the ineuphonious "muck." This 

 final stage of decomposition of ligneous tissue results in the formation of brown 

 matters which are known as ulmic compounds ; a further stage results in black 

 matter — humic substances : both of which classes are insoluble in water. Further 

 decomposition results in a soluble brown acid (apocrenic acid) and a colourless acid 

 (crenic acid). Although the chemistry of these bodies is so little understood, their 

 value in agriculture is universally recognised, and the application of decaying 

 vegetable substances to soils has from time immemorial been recognised as a fitting 

 treatment. 



By the generation of carbonic anhydride and ammonia (the first rendering 

 soluble and the latter supplying soluble plant-food) ; b}^ absorbing moisture from 

 the air, and thus keeping the soil damp ; by increasing the porosity of the soil, 

 so that in cases of exceptionally heavy rainfall the water may drain off, thus pre- 

 venting the crop from rotting ; by enabling more of the sun's heat to be absorbed, 

 owing to the black colour, and thus making the soil warmer — are some of the ways 

 in which humus benefits the land. 



Peat is generally understood to require stagnant water for its formation. The 

 aquatic plants growing on the surface of a pool in summer die in autumn and fall 

 to the bottom, and the pool, yearly becoming smaller, is eventually filled with plant- 

 remains, which then allow of the growth of Sphagnum and other mosses, and thus, 

 with a deficiency of oxygen, the moss finally becomes consolidated into a bed of 

 peat. One-seventh of the entire surface of Ireland, a basin-shaped country, low in 

 the interior and high at the coast, is covered with peat bogs. The growth of peat 

 is often comparatively rapid (5 in. or 6 in. a year is a common thing in Ireland), and 

 it is composed mainly of forms of plant-life such as Sphagnum mosses (a low order 

 of plants, having the faculty of continuing in growth upwards as they die below, 

 thus possibly enjoying an eternity of existence which may rank them among the 

 oldest of living plants) and Hypnum mosses, the former a calcifuge, the latter a 

 calciphile. Other plants, such as Eriophorum, Carex, Phragmites, Scirpus, Equisetum, 

 and heath-plants, such as Erica, are undoubtedly peat-formers, though they perform 

 their work more slowly. 



Hallmen, quoted by Nystrom (6), classifies peats as follows : Moss peat — 

 {a) Sphagnum peat, from Sphagnum moss ; (6) Hypnum peat, from Hypnum moss, 

 8 to 30 per cent, of ash ; (c) forest moss peat, from mosses, heath-plants, and the 

 residue of forests, 5 to 8 per cent, of ash. Grass peat — {a) Sea-peat, from Phragmites, 

 Scirpus, Equisetum, Menyanthes, Nymphaea, &c., 8 to 10 per cent, of ash ; (6) Carex, 

 from Carex family, mosses, and other plants ; (c) Eriophorum, from Eriophorum 

 (cotton sedge), 0-75 to 4 per cent, of ash. 



Bjorling and Gissing (8) point out that the formation of peat is dependent on 

 a special combination of climatic and topographical conditions, and state that the 

 principal factors are — {a) growth of aquatic and moisture-loving plants ; (6) a soil 

 or subsoil which will retain moisture at the surface ; (c) sufficiently humid atmo- 

 sphere to prevent too-rapid evaporation ; and (d) a temperature high enough to 

 allow a profuse growth of vegetation, yet low enough to check too rapid a decay 

 of vegetable matter. 



