PLANTS OF FRESH WATEK, SWASH'S, AND HOGS. HI 



Sphagnum possesses some characteristics which distinguish it from 

 most other mosses. Its stems at their periphery are provided with 

 thin-walled capillary cells, stiffened by fibrous thickenings, and com- 

 municating with one another and with the exterior by round open- 

 ino-s. Thus water is rapidly sucked in by the plant and stored up, 

 while, by the capillaries formed by the cells it can be conducted down- 

 wards to all parts of the plant. Although the surface on which the 

 sphagnum grows mav be extremely wet, but little water comes from 



_L O O * 



below, and then only for a very short distance. Thus a sphagnum 

 bog is altogether dependent on the rainfall, and can only exist where 

 this is abundant, an excessive precipitation allowing the plant to 

 occupy even a rock-surface. As the upper portion of a sphagnum 

 cushion grows, its lower part dies, and is converted into peat, great 

 masses of which frequently accumulate. Such peat is used for fuel 

 in many parts of the world, and at Waipahi, in Southland, is cut 

 for that purpose to some extent, though such New Zealand peat 

 is generally formed by many other plants in addition to sphagnum, 

 or this latter may be altogether wanting. The upper surface of a 

 sphagnum bog continues to rise in height, and any plants growing 

 thereon must, like dune vegetation, be able to grow upwards faster 

 than they are buried. The small pine, Dacrt/dium BidwiUii, com- 

 mon on subalpine bogs, is frequently buried by the too rapid growth 

 of the moss, and may be observed in all stages of burial. On the 

 sphagnum cushions themselves many plants will grow, owing to the 

 absorption of pure water, which cannot live on sour peat itself. 



Where a mountain-stream on flattish ground is unable to take 

 away all the water, an excess accumulates, and a bog is formed. In 

 such places shallow pools are frequent, between which are the sphagnum 

 hummocks. Here is the home of another cushion-plant, much re- 

 sembling Phyttachne, Donatia novae-zealandice, and a sedge of similar 

 habit, with leaves arranged like a comb, Oreobolus pectinatus. Other 

 plants occur in plenty e.g., a small celmisia (C. lonyifotia var. alpitift), 

 another with broader leaves (C. glandulosa}, the slender grass 

 Deijeuxia seti/olia, certain plants belonging to the rather rare family 

 Restionaceae, Gaimardia cili<it<i (fig. 53), G. setacea, and G. pallida, all 

 cushion-plants, and looking like mosses. Here, too, will be a dense 

 turf formed by a woody plant, Dacrt/dium lajri folium, that smallest 

 species in the world of the pine-tree family. 



